Fixed Issue #207:
Implement remaining API for getting flow state

NOTE: The implementation of the API backend is sub-optimal,
but should be sufficient for now:
  We fetch all flows, and then return only the subset that match
  the query conditions.
  We should use the appropriate Titan/Gremlin query to filter-out
  the flows as appropriate.

Estimated: 2D
Actual: 1D
8 files changed