Implement POST /api/1/composes to add new compose.
- New `builders` role has been added listing all the users/groups
who can create new compose.
- The ComposeInfo can be now send using POST to CTS which adds
it to the database and returns it back.
Merges: https://pagure.io/cts/pull-request/4
Signed-off-by: Jan Kaluza <jkaluza@redhat.com>