Draft implementation of grouping

Draft implementation of grouping

Grouping is done by creating group project and aggregating binaries
from submission projects into it.

Various checks for submissions have been implemented. Submissions
should have been published, they should not have common packages and
all grouped projects should have the same target project.

Note, that backend should be adjusted to build images for group
projects the same way as for submission projects.

Fixes: #1143

Change-Id: I5bdff34c951453707579579620bf3c28a0417d21
Signed-off-by: Ed Bartosh <eduard.bartosh@intel.com>
Reviewed-on: https://otctools.jf.intel.com/review/5900
Tested-by: OTC Tools Tester <ed.bartosh@linux.intel.com>