Closes gh-7214

Closes gh-7174
See gh-7213

Closes gh-7202

* pr/6954:
  Improve systemd service documentation

Closes gh-6954

Closes gh-7016

* pr/7043:
  Speed up Travis build

Modify to use standard mode and directory cache for Travis CI build.

Closes gh-7043

* pr/7193:
  Polish contribution
  Add a missing return

Add missing test

Closes gh-7193

This commit adds a missing`return` in `getDataSourceBeanDefinition()`.

See gh-7193

Closes gh-7208

* pr/6966:
  Remove unused

Closes gh-6966

* pr/7203:
  Correct typo in docs

Closes gh-7203

Update Cloud Foundry support with a discovery endpoint that shows what
endpoints are available.

See gh-7108

Add a CloudFoundryEndpointHandlerMapping that can expose actuator
endpoints for Cloud Foundry "appsmanager" to use.

See gh-7108

This commit switches off the auto-configured JspServlet's
development mode by default. Development mode is then switched on
when DevTools is on the class path.

Closes gh-7039

See gh-7197

ErrorPageFilter contained an optimisation for looking up the path
of an error page by exception type. For cases where there was no
mapping for the type of the exception that was thrown but there
was a mapping for one of its super classes, it was intended to
speed up the lookup. Unfortunately, there was a bug in the
implementation which meant that the optimisation had no effect.

Analysis with JMH reveals that for an Exception with a deep type
hierarchy, such as Spring Framework's UnsatisfiedDependencyException,
and an error page mapping for Exception, searching up the hierarchy
until a mapping is found takes 0.0000001s. With the same mapping,
a lookup for Exception takes 0.00000001s, i.e. it's 10x faster.
The optimisation, when correctly implemented, brings the time for
UnsatisfiedDependencyException down to 0.00000001s and into line
with a lookup for Exception. However, the amount of time involved is
so small compared to the overall time spent processing a request that
the added complexity of the optimisation is not justified.

Closes gh-7010

See gh-7101

Every classes that's compiled by Kotlin is annotated with
kotlin.Metadata. The attributes of this annotation always differ so
if they are used in the cache key, context caching will effectively
be disabled.

This commit updates the key used by ImportsContextCustomizer to
ignore the kotlin.Metadata annotation. Additionally, to align with
with Java where annotations in java.lang.annotation are ignored,
annotations in kotlin.annotation are also ignored.

Closes gh-7101

Closes gh-7112