(bug 45097) Introducing the Summary class.

The Summary class is to replace the Autocomment class. It can be used to
compose a machine readable auto-comment and summary for an action.

This change deprecates Autocomment, but does not replace it everywhere.

Credits for writing the Summary class go to John Blad, I just rescued it
from an abandoned commit.

Further work is needed to start using the Summary class everywhere.
Additional tests for checking the summaries would be nice.

Change-Id: I90c99198837f086aded16288c0bb3514d1565e9e
Merge "(bug 45097) Introducing the Summary class."