Update packaging to support webhook service and add dependency on lxml and (for Suse) python-South; also add migrations

Signed-off-by: David Greaves <david.greaves@jolla.com>
Add a webhook creation script: wh <project> <package> <git repo> [<branch>]

Signed-off-by: David Greaves <david.greaves@jolla.com>
Verify Project restrictions when handling incoming payloads; not just at validation

Signed-off-by: David Greaves <david.greaves@jolla.com>
Add some explanatory text for Projects

Signed-off-by: David Greaves <david.greaves@jolla.com>
Add migration for uniqueness constraint
Add cibot management to wh
Update process to use log_channel and default to #mer-boss (as per BUILD process)

Signed-off-by: David Greaves <david.greaves@jolla.com>