refactor(scope): separate controller from scope

Controller is standalone object, created using "new" operator, not messed up with scope anymore.
Instead, related scope is injected as $scope.

See design proposal: https://docs.google.com/document/pub?id=1SsgVj17ec6tnZEX3ugsvg0rVVR11wTso5Md-RdEmC0k

Closes #321
Closes #425

Breaks controller methods are not exported to scope automatically
Breaks Scope#$new() does not take controller as argument anymore