Closes gh-2697

Closes gh-2719

Closes gh-2951

Closes gh-2605

Closes gh-2760

Closes gh-2863

It was accidentally made public in 45b579c4.

Closes gh-2741

Closes gh-2946

Closes gh-2720

This commit adds CORS support to the Actuator’s MVC endpoints. CORS
support is disabled by default and is only enabled once the
endpoints.cors.allowed-origins property has been set.

The new properties to control the endpoints’ CORS configuration are:

endpoints.cors.allow-credentials
endpoints.cors.allowed-origins
endpoints.cors.allowed-methods
endpoints.cors.allowed-headers
endpoints.cors.exposed-headers

The changes to enable Jolokia-specific CORS support (57a51ed2) have been
reverted as part of this commit. This provides a consistent approach
to CORS configuration across all endpoints, rather than Jolokia using
its own configuration.

See gh-1987
Closes gh-2936

Work in 1b3efd41 actually introduced a regression: if a CacheManager is
created via a custom configuration file, it is no longer post-processed.

This commit makes sure to also customize a CacheManager that was
created that way.

See gh-2848

Without dependency management for org.apache.httpcomponents:httpcore,
it’s possible to get mismatched versions of httpcore and httpclient.

Closes gh-2941

Closes gh-2938

Closes gh-2934

Closes gh-2941

This avoids a potential problems with ordering between Dropwizard and
normal repository configuration. A Dropwizard sample has been added to
verify the behaviour.

Primarily when it is needed for metric export.

Adds a separate exporter per MetricWriter and allows individual
configuration of exporters for fine-grained control of schedules
and patterns etc.

Also fix bug in includes/excludes

Different physical sources for the same logical metric just need to
publish them with a period-separated prefix, and this reader will
aggregate (by truncating the metric names, dropping the prefix).

Very useful (for instance) if multiple application instances are
feeding to a central (e.g. redis) repository and you want to
display the results. Useful in conjunction with a
MetricReaderPublicMetrics for hooking up to the /metrics endpoint.

User can add a @Bean of type JmxMetricWriter and get all values
automatically exported in a form that is usable in jconsole
or jvisualvm.

Also rename Codahale* to Dropwizard* and move them to a new package

This seems pretty efficient (approx 12M write/s as opposed to 2M with
the DefaultCounterService). N.B. there is no need to change most of
the rest of the metrics stuff because metrics are write-often, read-
seldom, so we don't need high performance reads as much.

The Spring Integration configuration and Dropwizard support has changed
a bit. Functionally very similar and probably opaque to users, but now
the messaging operates as an Exporter on a @Scheduled method, and
Dropwizard is a replacement [Gauge,Counter]Service.

Metrics are all
collected live in-memory (and can be very fast with Java 8), buffered
there and shipped out to a MessageChannel (if one exists with id
"metricsChannel") in a background thread.

We can still use Java 8 library APIs (like LongAdder) but to compile
to java 7 compatible byte code we have to forgo the use of lambdas :-(
and shorthand generics (<>).

Fixes gh-2682, fixes gh-2513 (for Java 8 and Dropwizard users).

Expose the underlying cache infrastructure bean if Boot auto-configures
it. This is the case for ehCache, hazelcast and JCache. This change has
two side effects:

1. It is now possible to customize the underlying cache infrastructure
and let Boot only wrap it in the Spring's CacheManager abstraction. No
customizations are applied if the caching-specific service is customized
2. Such infrastructure is disposed when the application terminates as
it is now defined as `@Bean` and both `close()` and `shutdown()` methods
are invoked if present on the target type.

While the latter can be troublesome, we feel that a particular cache
instance is not meant to be shared and must be disposed when the
application terminates.

Closes gh-2848

Rework 155c60b7 to structure the code consistently, in particular with a more
natural order of attributes. Update test to use non-default values to ensure
that the customization has been applied.

See gh-2793

Update the CLI init command to expose additional attributes supported
by Spring Initializr. These are: groupId, artifactId, version, name,
description and language.

Closes gh-2793 and gh-2907

Document new configuration properties and remove redundant code

This commit adds support for configuring the JSP servlet’s init
parameters via the environment using server.jsp-servlet.init-parameters.*.
As part of this change the configuration of registerJspServlet and
jspServletClassName have been moved onto a new type, JspServlet, and the
existing setters on ConfigurableEmbeddedServletContainer have been 
deprecated. In addition to providing a model for configuring the JSP
servlet that’s consistent with the model for other configuration (SSL,
for example), this change also means that the class name and whether or
not the servlet is registered at all can now also be configured via the
environment.

Closes gh-2825

Some of the features of the launch.script were not exposed for users
to be able to control at runtime. It now accepts things like
PID_FOLDER and LOG_FOLDER as environment variables, and also adopts
a clear naming convention where only the inputs are UPPER_CASE.