Add willPrepareForDraw to Component.

This is the last moment before the component's element is replace by its
template if he has one.
Remove didSetElement for RootComponent
Move attribute to Component

Mostly this is code from native-control
Functionality isn't changed at this point
Remove class attribute
Moving textContent handling to Component.

This doesn't add textContent to all components but allows subtypes to
use this functionality.
Fix a few jasmine matchers
Fix popup-spec
Merge pull request #1101 from francoisfrisch/native-control

Conflicts:
	ui/component.js