docs(Angular.js): explain that toJson strips $... properties

In Angular.toJson, any properties with a leading '$' character will be
stripped from the resulting string since angular uses this notation
internally for services.  There have been complaints of not knowing
about this functionality until it breaks within their code.
docs($cacheFactory): show that you can access existing caches
chore: add karma-script-launcher plugin

This plugin is shipped as a default one with Karma. It's specified as a peer dependency.

I assume, there's an old version of NPM on the CI server, which does not support peerDependencies and therefore it didn't get installed.

This will make the dependency explicit.
docs(guide/location): fix example code - `hashPrefix` is a method
chore(travis): speed up the build

- parallelize the tasks
- cache requests (e2e tests)

This reduces the time from ~18min to ~12min.

It makes the output little messy. We could buffer output of each task and display it once it's fully finished, nicely. I think giving instant feedback is better.

Conflicts:
	Gruntfile.js
	package.json