Relocate `SpringBootPlugin` to fix a package tangle.

Fixes gh-6355

Closes gh-6360

Closes gh-6369

Closes gh-6008

Closes gh-6357

Previously, the shutdown endpoint would spawn a new thread to perform
the shutdown but did not explicitly configure its thread context
class loader (TCCL). This mean that the new thread would use the
request thread's TCCL as its TCCL. This meant that a different TCCL
would be used compared to a shutdown triggered by the shutdown hook
and also caused problems with Tomcat's thread leak detection logic.

This commit updates the shutdown endpoint to explicitly configure the
TCCL of the shutdown thread to be the ClassLoader that loaded the
endpoint's class.

Closes gh-6361

Closes gh-4892

Previously, the shutdown endpoint would spawn a new thread to perform
the shutdown but did not explicitly configure its thread context
class loader (TCCL). This mean that the new thread would use the
request thread's TCCL as its TCCL. This meant that a different TCCL
would be used compared to a shutdown triggered by the shutdown hook
and also caused problems with Tomcat's thread leak detection logic.

This commit updates the shutdown endpoint to explicitly configure the
TCCL of the shutdown thread to be the ClassLoader that loaded the
endpoint's class.

Closes gh-6361

Closes gh-6358

* pr/6365:
  Upgrade to Spring Integration Java DSL 1.1.3.RELEASE

Closes gh-6365

Closes gh-6344

* pr/6350:
  Upgrade to Spring Security 4.1.1.RELEASE

Closes gh-6350

Closes gh-6340

Commit 3ea84f9e has wrongly introduced a `@Primary` marker on
`IntegrationMBeanExporter` so any use of both Spring's JMX support
and Spring Integration's JMX support leads to an exception. This commit
makes sure to remove the unnecessary `@Primary`

Closes gh-6328

Closes gh-6331

This commit makes sure to use `getAliasedStringArray` rather than
`getStringArray` as the latter does not work with ASM. While this will
probably be fixed in the core framework, this commit also adds dedicated
tests with ASM to ensure that the code works as expected.

Closes gh-6337

This reverts commit 7bb39f82.

Unfortunately the mirror seems incomplete

Add mirror setting so that a full build uses the Google mirror of Maven
Central.

Update WebRequestTraceFilter so that additional post processing can be
applied to traced request headers. The postProcessRequestHeaders method
can be used to remove or change map entries before they are returned.

Fixes gh-6309

Align DataSourceInitializer to Spring Framework by lexically sorting
resolved resource patterns.

Fixes gh-6316

Fixes gh-6343

* jsf-spring-boot-starter-1.6.1:
  Update starters readme with updated JSF support

Update readme since jsf-spring-boot-starter 1.6.1 added support for
BootsFaces and AngularFaces.

Closes gh-6342

* issues/6320-mockito-2.0.47-compatibility:
  Fix compatibility with Mockito 2.0

Update MockDefinition to only call `Answers.get()` if a direct cast
isn't possible. This provides compatibility with Mockito 2.0 (currently
2.0.47-beta) without breaking support for Mockto 1.x.

Closes gh-6323

Previously, an entry had to be added to spring.factories using the
name of one of the @AutoConfigure… meta-annotations on the @…Test
annotation as the key. This indirection was unnecessarily complicated.

This commit simplifies things by allowing the name of the @…Test
annotation itself to be used as the key.

Closes gh-6335

See gh-6318

Closes gh-6332

Closes gh-6044

Closes gh-6325