Ractive

I propose we replace AngularJS + jQuery with RactiveJS for UI templating and data binding.

### Pros
- Reduced file size. The JS bundle is reduced from 3.7M to 1.4M (150K to 87K minified + gzipped). The client downloads less data and executes less code.
- Less `$scope.$apply` boilerplate.

### Cons
- Relearning things.
- Less external libraries ready-to-use.
- Maintenance of Ractive is by a small group of people, while AngularJS is maintained by Google.