SideBySide2: Scroll to first diff chunk when opening view

If the first diff chunk is not within the visible region, scroll
to make it visible in the middle of the editor. When a large file
is opened with context set to whole file this saves a lot of time
trying to get to that first edit.

Change-Id: Ie659ecddc03bc9a5b81d2ffcc4175424a9cddcca
Fix disable of new features in ChangeTable2

Columns were incorrectly computed in a few locations.

Change-Id: Icab52737de8aa18e62d18f30f6973a34ab8c5344
Merge "SideBySide2: Scroll to first diff chunk when opening view"