feat(scope): move domWrite and domRead from RootScope to Scope

Closes #1161

Closes #1341
refactor(ngClass): drop unneeded closures
style(ngModel): Drop unneeded "this." prefixes
refactor(ngSwitch): simplify the code

- scope was not needed in _ViewScopePair any more,
- drop _ViewScopePair, storing a ViewPort only is enough thanks to its
removeAll() method

Closes #1389