inserting webhook key in separate table
Deleting from webhook keys table when deleting single webhook
Delete webhook keys when deleting group
webhook_keys table removal when deleting group

Also made deletion query global since it was used in other places
Returning queries and params instead of mutating - per @radix
removed unwanted comment - thanks @cyli
clearer comments - for @radix :)
reordering query args based on schema - thanks @cyli
Merge pull request #698 from rackerlabs/as-222-webhook-table

AS-222 webhook keys table insert and delete
Merge pull request #699 from rackerlabs/convergence-model

Data-model for convergence.
Some functional goodies for Otter

- depend on pyrsistent
- add freeze and unfreeze functions to otter.util.fp
  (to be contributed to pyrsistent)
- add "partition_bool" and "partition_group" functions to otter.util.fp
  (to be used by convergence)
Merge branch 'otter-is-functional' into converge-function