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.
Fix WikiController test_update_stale_page_should_not_raise_an_error

The test didn't specify the version it depended on, so its assertion failed.

I have no idea why the second changed assertion ever worked, since the
journal's version should never change. This restores the line as it
was before commit c25bbee177dbb71d983ff78ab528889a6ba4bec5.
Merge branch 'fix/wp_journal_not_added' into release/3.0