Add `commit-msg` hook that requires referencing a GitHub issue number

[Robbert]

Initially I thought this should be a pre-commit hook, but I learned that there is a special hook called commit-msg for this purpose.

The plan:

• [x] Check if the commit message contains /#(\d+)/
• [x] When no number is added, check if the branch is named /(issue|bug|feature)-(\d+): if so, append #123 to the commit message.
• [ ] Check if the issue exists in the ./{issue} exists relative to the bugs.url location from package.json, at least when the URL matches //github.com/{user}/{repo}/issues.

[Robbert]

I'll put the github.com issue check task on the backburner.

For private repo's I suppose this would require using API tokens for authorization.

[Robbert]

We should have test for the regular expression. It should allow these:

• Fix #42
• Fix user/repo#42

[Robbert]

We need to test the pattern to allow these:

• Fix #55
• Fix wesanih/incubator#55