Unembed mGerrit from ROMControl

Completely separate mGerrit from ROMControl. If mGerrit is not
installed fallover to PlayStore installation of mGerrit.

Patch Set 2: Fix duplicate intent launching

Change-Id: Ie19ca595026fcdbb2cfd8dacc5e553b058b1a8c1

Conflicts:
	AndroidManifest.xml

Change-Id: Ie19ca595026fcdbb2cfd8dacc5e553b058b1a8c1