Rationalize the Reactor autoconfig

It didn't make sense not to do anything at all if a Reactor @Bean
was detected, so now we only back off creating the rootReactor if
one is present.
Added Janino to BOM.
Merge pull request #1016 from hekonsek/bom-janino

* bom-janino:
  Added Janino to BOM.
Add a note regarding dependency overriding

Fixes gh-958
Fix broken links in the documentation
Merge branch '1.0.x'
Auto-generate auto configuration classes tables
Fix section title depth in JMS docs
Make DataSourceInitialization a no-op if there is no DataSource

Fixes gh-1041
Make late Environment changes appear in ConfigurationProperties
Disable HornetQ by default for testing
Remove dead code in ServerProperties
Add tests to verify starter dependencies when used with Gradle

We've had problems with the starters when used with Gradle. They have
been pulling in commons-logging (#987) and the wrong version of Spring
(#1028) due to Gradle's different exclusion and dependency resolution
semantics.

This commit adds some integration tests that use Gradle's tooling API
to take each starter in turn and build a Gradle project that depends
upon it. The build looks at the transitive dependencies and checks
that neither commons-logging nor any Spring modules with the wrong
version are present.

Closes #1036
Add @ConditionalOnJava

Added a new @ConditionalOnJava annotation that allows to conditionally
enable configuration based on the Java version that is running. 

The annotation currently supports two modes of restricting Java versions:
the default mode checks for a Java version equal or better than the
requested one. Beyond that it can be configured to only match if Java
version is older than the configured one.
Add auto-configuration for Jackson's JodaTime and JSR-310 modules

We now register the Jackson JodaTime module with Jackson ObjectMappers
if it is on the classpath. We also register the JSR-310 module if it's
on the classpath and the application is running Java 8 or better.

Extracted the Jackson specific configuration previously residing in
HttpMessageConvertersAutoConfiguration into a JacksonAutoConfiguration
class.

Added the Jackson JSR-310 module as a managed Boot dependency.
Align expectations of various JMX configurations

They all want to create an MBeanServer and when that happens
user sees no MBeans, or sometimes just one set (Spring Core,
Spring Integration or Spring Boot). To harmonise them we
create a @Bean of type MBeanServer and link to it in the
other autoconfigs

Fixes gh-1046
Fix duplicate id in the docs