Use bower for vendor assets

:construction: :construction: :construction:

Currently we're just storing vendor assets in source control this introduces bower and [bower-rails](https://github.com/42dev/bower-rails) to manage asset dependencies for Supermarket.

~~This also introduces Angular as I think we've been struggling with adding rich user interaction without writing spaghetti jQuery code. I think Angular will allow us to still render mostly on the server but provide the opportunities for greater interactivity. Introducing Angular is actually what drove introducing dependency management as I think we should take JS more serious in this project in general.~~

Worth also noting that I have noticed and @danvolkens has also probably noticed even more :smile: that SCSS compilation is a tad bit slow with sprockets. Probably won't happen in this PR but I'm wondering if [broccoli](https://github.com/joliss/broccoli) is worth exploring as it accomplishes basically what the asset pipeline accomplishes but with speed.

### Todo

- [ ] Ensure Vagrant works with bower.
- [ ] Ensure Travis CI works with bower.
- [ ] Ensure Supermarket recipe works with bower.
- [ ] Ensure how to use bower is documented.
- [x] Determine how to force a jQuery version.