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.