[bug 1108755] Add a git commit message linter

As mentioned in the comments of bug 1108755 as requirements,
the commit message linter does the following things:

1. Enforces max. 79 characters per line
2. Verifies the summary line has bug numbers in the right format
3. Does a bugzilla lookup for the bug and prints out the 'bug id',
   'summary' and 'assigned to' fields.
I'm on the fence about requiring 79 characters or less. I think there are instances where I've blown over that. It doesn't display well in some tools, but sometimes for clarity purposes it's important.

Having said that, this hook doesn't return a non-0 exit code so it's not like other hooks where it blocks things from happening when there are issues. So maybe this is fine.