Move hooks & service integration in a lib module

[La0]

This is the first step towards creating a pulselistener library (name to be determined...)

In src/pulselistener/pulselistener/lib there should be:

• phabricator.py managing communication with Phabricator
• mercurial.py managing mercurial clones, patch application & pushes
• web.py managing a web server to receive HTTP requests
• pulse.py managing pulse hooks to receive messages on defined queues
• bus.py to create a new communication bus to send/receive messages across above parts

[La0]

The #2193 PR is too big to review / test properly, i'm splitting that work in several chunks:

1. do not use cli_common anymore so we have a clean base for future split. #2222
2. add the message bus class + use it for webserver only #2223
3. move monitoring in lib, using message bus #2227
4. move phabricator in lib, using message bus #2236
5. move mercurial in lib, using message bus #2236
6. split workflows

Each step will be run on testing/staging

[La0]

This is done: https://github.com/mozilla/libmozevent