Cover main functionality with tests

[gorbunkov]

We must cover most critical functionality with tests. For example it may be:

• AnnotatedIndexDefinitionProcessor - index configuration creation using annotated classes, see how annotated configurations are parsed

• Indexed entity changes listeners - create/modify entities and check that a record appear or don't appear in the indexing queue

• Indexing of entities with various PK types (including composite)

• Maybe even tests with running Elasticsearch server - check that documents with desired structure appear in index

• etc.

• Index Definition processing tests

• Entity change tracking tests

• Entity indexing tests