Added some fixes in the journalization of document modification:

 - Fix that separte metadata changes are journalized as metadata changes now instead as `file and metadata` changes .
 - Always create a separate journal entry for public_trial changes
 - When changing only the public_trial, don't create an entry for metadata changes.
 - Reworked tests for the document modification journalization.
Fixed templatedossier tests.

With the fix https://github.com/4teamwork/ftw.testbrowser/pull/17,
the ftw.testbrowser handles the checkbox now correctly, so some changes in the
templatedossier tests was necessary.
Merge pull request #462 from 4teamwork/pg_document_journalization

Added some fixes in the journalization of document modification: