Polish DataSourceInitialization code

Rename a few classes and methods relating to DataSourceInitialization
and update the DataSourceInitializedPublisher to check for Hibernate
settings.
Polish documentation

Apply consistent styling and edit a few section for clarity.
Add gmavenplus-plugin to parent POM
Convert README.md -> README.adoc
Polish ConditionalOnJava

Apply formating and simplify the condition implementation. Delegate
to Spring's JdkVersion class to obtain the running version.
Polish Flyway and Liquibase

Extract common "depends on" functionality to a new
EntityManagerFactoryDependsOnPostProcessor class.

Apply consistent formatting.

Fix issue with Flyway location detection.
Polish