Add "repo overview" command.

The overview command shows an overview of each branch in all (or the
specified) projects.  The overview lists any local commits that have
not yet been merged into the project.

The report output is inspired by the report displayed following a
"repo prune" event, with the addition of listing the one-line log
messages for each commit that is not yet merged.

The report can also be filtered to show only active branches; by
default all branches that have commits beyond the upstream HEAD will
be listed.

Change-Id: Ibe67793991ad1aa38de3bc9747de4ba64e5591aa
1 file changed