[REVIEW ONLY] Automaticlly get latest Bootstrap version w/fallback

I do not know if this makes any sense, as I have never used Bootstrap myself, but I thought it would be an interesting idea. Uses the GitHub API to get the latest version.

Of course, a fallback is also specified (set to the current latest version).

This is built on top of #9, thus I labeled it as Review Only. If you like what you see, I will rebase this against master once the other PR is merged. :wink:

Also, I am not done submitting changes yet! I have more for you, but they will have to wait until you approve #9 (as it laid part of the foundation needed).