Rename SQL script annotations in the TCF

Prior to this commit, SQL script annotations and related classes in the
TestContext framework (TCF) were named DatabaseInitializer*. However,
these annotations are not used only for initialization and are
therefore misleading when used for cleaning up the database.

This commit refines the names of annotations and related classes for
configuring SQL scripts to be executed for integration tests in the TCF
as follows:

- @DatabaseInitializer -> @Sql
- @DatabaseInitializers -> @SqlGroup
- DatabaseInitializerTestExecutionListener -> SqlScriptsTestExecutionListener

A special thanks goes out to the following attendees of the Zurich
Hackergarten meeting last night for their collective brainstorming:
@aalmiray, @atsticks, @ollin, @simkuenzi, @tangresh, @vyazelenko.

Issue: SPR-7655
Introduce repeatable @Sql tests

This commit introduces explicit integration tests that verify Java 8's
@Repeatable support for the @Sql annotation.

Issue: SPR-7655