Remove dependency on python git module.

It was not actually doing anything useful for us anyway.
Send replies to http requests.

This avoids constant message from the trac backend that the http response
has not started after the hook as been run.
Update hook to use standard github webhook with json encoded data

Avoids needing the special trac service.
Use unicode strings rather than plain ascii

Also deal with a push that may have no commits in it, i.e a branch deletion
Hook moves ticket to verify when a pull request is opened.

It uses the github api to retrieve full name of the user from their
github name.
Also added a test payload for a pull request
Improve testing script to allow selection of payload type.
Normalize case usage in method names.
Assigning/unassinging pull requests alters ticket state accordingly
Merge branch 'feature/std_github_webhook'