Add `bst source` command group
Background
See https://mail.gnome.org/archives/buildstream-list/2018-November/msg00106.html and its replies for full context. The summary is that similar to how we plan on having a bst artifact
command group to handle all operations related to artifacts, it would make sense to have a bst source
command group to handle all source operations.
Task description
-
Add new source command group -
Move fetch, track and source-checkout commands under the new group -
Mark fetch and track commands as obsolete
Acceptance Criteria
Edited by Chandan Singh