Minor Refactoring of Resource Aware Scheduler

Refactored the following:

1. The API interface to define custom scheduling strategies. The API exposed from RAS to a per topology scheduling strategy is messy and needs to be cleaned up.
2. In RAS, the state of the scheduler is held by several member variables. Its cleaner if the scheduler state is represented by a single object. This will help we reduce the amount of code need when checkpointing the state of the scheduler and potentially restoring the state in the future when a bad scheduling happens