Persisting users diff formatting preferences

When a user changes diff formatting preferences and clicks the
Update button the preferences will then be persisted in the database.
This way a user doesn't have to adjust the diff formatting
preferences each time it switches to the next file diff.

Bug: issue 579
Change-Id: I52cd1dcf702ed04046b236228f994fb9042243d9
Signed-off-by: Sasa Zivkov <sasa.zivkov@sap.com>
25 files changed