Fixes gh-2110

Closes gh-2021

Update DEFAULT_SESSION_TIMEOUT to use TimeUnit.MINUTES.toSeconds(30)
rather than TimeUnit.SECONDS.toMinutes(30) which would always return
0.

See gh-2084
(cherry picked from commit b33bbd56)

Update AbstractConfigurableEmbeddedServletContainer to set the default
session timeout to 30 minutes. Also correct Javadoc to specify that
the default is '30 minutes'.

Fixes gh-2084

Add a tip for both the Maven and Gradle "Packaging executable jar and
war files" section referring to the how-to.

Fixes gh-2086

See gh-2080

Partly back port changes from affb202e and 85c95744 to fix the usage
of JMS in the CLI. Restore the integration test using HornetQ and fix the
coordinates of the JMS API.

Fixes gh-2075

Extract some of the common property keys as constants.

Fixes gh-2068

Replace `classpath:db/migrations` with `classpath:db/migrations`.

Fixes gh-2063

SecurityAutoConfiguration, via its import of
AuthenticationManagerConfiguration, requires spring-security-config
to be on the classpath as AuthenticationManagerConfiguration extends
GlobalAuthenticationConfigurerAdapter from spring-security-config.

This commit makes SecurityAutoConfiguration conditional on the
presence of GlobalAuthenticationConfigurerAdapter so that the
auto-configuration will be disabled in its absence rather than causing
an app to fail to start.

Closes gh-2046

See gh-1995

Change the visibility of ErrorPageFilter to public to fix
IllegalAccessException errors on certain servlet containers.

Fixes gh-2026

Use putIfAbsent to ensure atomic creation of lock objects.

Fixes gh-1995

Previously, the host had to have a custom value for the configuration
of the port or credentials (username and password) to take effect. This
meant, for example, that you couldn’t just set the port or just set the
username and password while using the default host.

This commit allows the port or username and password to be configured
without also configuring the host. The default host (localhost) and
port (27017) are retained.

Fixes gh-2008

Closes gh-1989

In a properties file, a backslash is used as an escape character for
the line terminator sequence to allow values to be split across
multiple lines. When a backslash is used elsewhere they're stripped
out of the property's value.

This commit updates .properties-based examples for configuring
server.tomcat.internal-proxies to escape the backslahes so that they
are retained in the property's value at runtime.

See gh-1989

Closes gh-1998

Closes gh-1908

Previously, index.html used absolute paths to load its CSS and
JavaScript. This meant that it had to be deployed to /. This commit
updates the HTML to use relative paths for its CSS and JavaScript,
thereby ensuring that they can be loaded irrespective of the context
path to which the application is deployed.

Closes gh-1988

(cherry picked from commit d4bf221f)

Fixes a couple of typos in the documentation:
* `x-forwarded-protocol` is not the standard name for this header
* `require_https` is not an existing property, but rather `require_ssl`

Some environments do not have a tmpdir so it can be null.

Previously, if Logback was being used as Boot's logging system, but
Log4J was also on the classpath before SLF4J and Logback, JBoss
Logging would use Log4J for its logging. This lead to warning messages
being produced as Log4J was not configured:

log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.

This commit updates LogbackLoggingSystem to set the
org.jboss.logging.provider to "slf4j". This ensure that JBoss Logging
will use SLF4J and Logback as intended even when Log4J is also on the
classpath.

Closes gh-1928

Add LICENSE.txt file and make it clear in the README file that we
are Apache 2.0

Fixes gh-1952

Fixes gh-1948

Closes gh-1919

Previously, only the http.mappers.json-sort-keys property was applied
by JacksonAutoConfiguration. This commit updates it to also apply the
http.mappers.json-pretty-print property as well.

See #1919

Closes gh-1936

Closes gh-1906

Closes gh-1905

Fixes gh-1944

Previously, for a non-async response with a successful status (< 400),
ErrorPageFilter would always call flushBuffer. This triggers an
exception in Tomcat if the client has closed the connection before the
response has been fully sent. In this case, Tomcat treats the response
as successful and commits it before control returns to the filter.

This commit updates ErrorPageFilter to only perform the flush if the
response has not already been committed, leaving any further flushing
that may be necessary to be handled by the servlet container.

Fixes gh-1938

Update ConfigurationPropertiesReportEndpoint to find
@ConfigurationProperties using `context.findAnnotationOnBean` rather
than `AnnotationUtils.findAnnotation`. This will correctly find the
annotation even if the bean is an interface based proxy.

Fixes gh-1927