mGerrit: Introduce stalker mode

Long clicking on any name associated with a gravatar image
will bring up a context menu where you can view changes the
selected user has contributed;

You can see only their submitted code (Owner of commit)
or
You can view the commits with the user tagged as a reviewer
(could be from commenting on code or someone tagging the user
as a reviewer)

Change-Id: I7dedeff2bb98bc989b7aaf024a19899fd7300762
Merge "mGerrit: Introduce stalker mode"