Clean up acts_as_journalized SaveHooks
acts_as_journalized: Use save! instead of save

This should prevent journals silently not being saved on validations
errors.
JournalManager: Fix attempting to create two journals with same version

Calculate journal version based on existing maximum instead of count.

Up to now, when removing a journal note with another journal entry
existing afterwards, there could be a single journal with version 2,
resulting in validation errors for the next attempt to add a journal.