Initial Metis implementation

Summary:
Remaining shit:

  # Scheduling ability using Chronos.
  # Ability to write output to Kronos stream (requires delete implementation to be landed first)
  # Semantics + implementation of transforms with no aggregates.
  # Validation of transforms to ensure we have proper ordering of operations.

Reviewers: marcua, meelap

Reviewed By: meelap

Differential Revision: http://phabricator.locu.com/D3158