Implementation of typed two-parted scheduler

[sebastian-peter]

Resolves #378

Some notes:
The new scheduler only stores one activation for an actor at a time.
This also means that trigger revocation happens automatically.

Adjacent changes are the following:

• CompletionMessage can only contain one trigger and should only schedule the completing actor. For other schedulings, the ScheduleTriggerMessage is used (for now)
• Removed actor reference from TriggerWithIdMessage, which has never been used

This is another step to move the scheduling mechanism in SIMONA more towards DEVS. There's more to come.

[danielfeismann]

Thanks for your work especially for keeping ScalaDoc updated here as well. I mainly would like to double check if the todos are for the upcoming work - I least I guess so - and have some little questions.

[danielfeismann]

LGTM, thanks :)