Allow projects to be specified as notdefault

Instead of every group being in the group "default", every project
is now in the group "all".   A group that should not be downloaded
by default may be added to the group "notdefault".

This allows all group names to be positive (instead of removing groups
directly in the manifest with -default) and offers a clear way of
selecting every project (--groups all).

Change-Id: I99cd70309adb1f8460db3bbc6eff46bdcd22256f
5 files changed