Don’t show / hide views in layout. Closes gh-528.
Add View#keepElement.

If it’s true, $el.remove() won’t be called. Instead, all events will be unbound from view.
Inherit Layout from View, bind it to body instead of document. Rename methods.

 Renamed Layout methods and properties:
	* `_registeredRegions` to `globalRegions`
	* `registerRegion` to `registerGlobalRegion`
	* `registerRegion` to `registerGlobalRegions`
	* `unregisterRegion` to `unregisterGlobalRegions`
	* `unregisterRegions` to `unregisterGlobalRegions`

Removed layout events spec as it’s not needed because we have same view spec.

We had enough borrowed methods from View in Layout so just inheriting it will be cooler.
Merge pull request #545 from chaplinjs/topics/layout-changes

Massive layout changes