Add more Git hooks, delegate to .local convention

The `pre-commit` and `prepare-commit-msg` git hooks can be used for some
interesting things such as linting files. For example:

https://github.com/croaky/dotfiles/commit/b3bc7d3f0dff46a47697c8c81a8352b76eb0e3a5
I think if you don't have a `.git_template.local/hooks/prepare-commit-msg`, this if statement will fail, and the commit will fail due an a non `0` exit status. I was bitten by this while creating https://github.com/thoughtbot/dotfiles/pull/284