feat(ScopeAware): Introduce ScopeAware abstract class.

Components that implement the ScopeAware scope setter, will get scope
set during compilation.

Currently, there is little incentive to use this, because Scope can be
injected in the Components. However, after PR/1269 Scope would not be
injectable and this would be the only way for components to obtain
scope.

Introducing this API earlier allows for clients to start using it and
not break when PR/1269 lands.