Use Angular

This replaces the ugly jQuery-based UIs for tokens, etc. with much cleaner Angular apps.

It also provides some nice equipment to make it easy to include an Angular app in a view function.  Basically, a page can be *either* a Jinja2 template (rare, except core stuff) or an Angular template (more common for UIs).

I learned the hard way, by trying and failing twice, that you can't really mix the two, and that you can't mix source from more than one blueprint in a single page -- in particular, implementing the root widgets using AngularJS is not practical (see https://github.com/djmitche/build-relengapi/tree/angular-root-widgets).

I hope that the docs are actually *more* understandable than before.  I realize that Angular's not a common tool among releng, but I think it can become one.