add translated documents lifecycle events, pre-/postBindTranslation and ...

This PR will hopefully cleanup #474.

I created a the following events:
- `preBindTranslation`
- `postBindTranslation`
- `loadTranslation`

and separated the test for the translation stuff. pre- and postBindTranslation surround the process when binding the translation and setting the document's translatable properties to that hash map in the UnitOfWork. loadTranslation is fired when all translation loading is done, means all cascading stuff.

@dbu is it the way you thought about it? Just did not understand your question about implicit/explicit. Can you explain what you mean, please?