Closes gh-1739

If a Gradle build is using the Spring Boot Gradle plugin's support for
declaring dependencies without versions then they will be unable to
publish Maven artifacts from the build as the Gradle-generated pom
will fail to validate. This is because Gradle doesn't apply the
Boot-provided dependency versions to the dependencies in the generated
pom.

This can be addressed by configuring Gradle to generate a pom that
either imports spring-boot-dependencies into its dependency management
or that uses spring-boot-starter-parent as its parent. This commit
updates the documentation to document the need for this configuration
and to provide examples of how to do so.

Closes gh-1806

Traditionally, a @ServerEndpoint-annotated bean is found by a servlet
container initialiser, however Boot does not run servlet container
initialisers when an embedded container is being used. To be able to use
@ServerEndpoint in a Boot app that uses embedded Tomcat a
ServerEndpointExporter bean must be declared.

This commit updates the documentation to describe this requirement and
also updates the WebSockets sample to illustrate the use of
ServerEndpointExporter. The version of Spring Framework has been updated
to 4.0.8.BUILD-SNAPSHOT. This picks up the fix for SPR-12340.

Closes gh-1722

Closes gh-1861

Relocate tomcat-embed-websocket from spring-boot-starter-websocket
to spring-boot-starter-tomcat.

Fixes gh-1847

Fixes gh-1834

Fix an issue where debug logging never occurred because it was guarded
incorrectly using isWarnEnabled().

Fixes gh-1780

Some were missing, some were named incorrectly.

See gh-1827

Update ManagementSecurityAutoConfiguration to return
IgnoredPathsWebSecurityConfigurerAdapter rather than
WebSecurityConfigurer<WebSecurity>.

Instead of just blindly creating the default authentication manager, after
thic change we count the beans of type GlobalAuthenticationManagerConfigurer
and assume that if we detect more than we expect (one from Boot and one from
Spring Security) then the user is telling us they want to configure the
AuthenticationManager themselves.

Fixes gh-1801

GroovyWebConfiguration creates a GroovyTemplateViewResolver which is
a UrlBasedViewResolver sub-class. UrlBasedViewResolver is provided
by spring-webmvc. Previously, if a user configured a web application
but did not have spring-webmvc on the classpath, the application
would fail to start with a NoClassDefFoundError for
UrlBasedViewResolver.

This commit makes GroovyWebConfiguration conditional on
UrlBasedViewResolver being on the classpath so that it backs of in
the absence of spring-webmvc.

Fixes gh-1793

Closes gh-1787

Closes gh-1774

Closes gh-1782

Fixes gh-1753

Closes gh-1708

Closes gh-1742

Closes gh-1740

Previously, there was a timing window where the output file had been
created but it was empty. This would cause the test to fail as the
output was read from the empty file and didn’t match the expected “Hello
World”.

This commit updates the test to only process the resources in the output
directory when all the resolved resources have a non-zero content
length. An @Before method has also been added to delete the output
produced by the test so that the outcome of the test isn’t affected by
files generated by previous runs.

Fixes gh-1735

Maven is configured to run tests found in classes ending in Tests.
This meant that the tests in BasicErrorControllerIntegrationTest (note
the missing s) were not being run.

This commit renames the test class so that it's picked up by Maven.

Closes gh-1710

This reverts commit 26a528ce.

Fixes gh-1706

Fixes gh-1693

Update `Launcher` and `JarFile` to correctly deal with Windows UNC
paths.

Fixes gh-1641

When logging.level.* is set in external configuration they can now
contain placeholders.

Fixes gh-1680

Closes gh-1671