Design and implement BehaviorModel interface

[ChrisTimperley]

We should add a BehaviorModel class to abstract away the implementation details of how behavioral models work and to provide a interface for tools to hook into.

Below is a partial example of what a BehaviorModel could potentially look like.

class BehaviorModel(object):
  @staticmethod
  def from_file(self, filename: str) -> 'BehaviorModel':
    ...

  def to_file(self, filename: str) -> None:
    ...

  def score(self, trace: MissionTrace) -> float:
    ...

  def validate(self, trace: MissionTrace, threshold: float = 0.05) -> bool:
    return 1 - self.score(trace) > threshold