Create a new default factory for Dynamic services which doesn't attempt to create a new service

[brunocoimbrar]

Introduce two new default factories:

• DefaultDynamicServiceFactory: for non-Actor service with DynamicService attribute, which will return null by default instead of creating a new instance (assumes that Set will be called eventually).
• DefaultDynamicServiceActorFactory: for any Actor service with DynamicService attribute, which will try to find the Actor and return null if none is found, instead of creating a new instance.

Will require adaption to code generator to handle those cases.