feat(directives): remove the @Controller directive

Completely remove the deprecated Controller directive. Update the
demos to use setRootContext.

Pulled out of the first commit in #1269.
Currently, the examples don't use components. My PR extracts the controller code into a component, which means previously we had one big index.html, now we have index.html and component template html.

The way expression extractor works is that the entry points are all web/*.dart files, from there we find all web/*.html files that reference them (that's how index.html is picked up) and all templateUrl: are extracted from annotations and the right files are found (that's how packages/angular_demo_example/bouncing_controller.html is picked up).

The extractor has issues with relative paths as the extractor resolves relative to the package root, but the web server works relative to web/. @chirayuk  is saying that this should be fixed very soon (so we can change this).