Started scheduler schema change

Events stored based on minute they will execute.
future time check in minute
started bucket based impl
in middle impl
scheduler methods outside the class - pure :)
Merge branch 'master' into buckets

Conflicts:
	otter/models/cass.py
	otter/scheduler.py

Taking scheduler newer code
Scheduler test case methods added

Just need to implement them :)
reverted json_schema changes
Scheduler tests working
was not giving set to partition - fixed

- giving list of buckets to store and it'll cycle over it
- Some comments in scheduler.py
lint fixes
model change related to scheduler

policy table has version column that gets updated whenever its
respective event is added to event table. scheduler ensures that version
matches before executing event. This way, we dont bother deleting event
whenever a policy is deleted or updated. When a policy is updated, a new
event with new version is added. The old event when picked up will not
get executed since its respective policy (with that version) is not
there. Added version=None to get_policy that checks the version before
returning.

Refactored test_cass_models into seperate class for testing add_policy
and update_policy
Not deleting events on group delete
mock models fixed
Version is updated only when policy is updated/insert

When an event is added, it is added with current policy version. This
way there is no dependency from event to policy table
Calling correct SetPartitioner instead of incorrect SetPartition
tap/api.c tests added - need more
model cleanup code - thanks @cyli
scheduler doc changes - thanks @cyli
Unitgration tests - Not backing up previous keyspace

as UUID1 is not json serializable