Rework migration to use both pymongo and of core.db
  - Remove all references to `capped_size` in buckets collection
  - Copy down all realtime buckets into newly capped collections (at 4mb)
  - Add in new reference to `capped_size` in buckets collection
Check if collections have a cap on them before running
ensure we have stats before testing properties of those stats!
Be more specific about collection names and give better logging
is not the same as
Be more specific about which capped references to remove
Refactor to make steps clearer and remove reset

- Break out steps to make the process clearer
- Remove pre step of resetting metadata
- Add pre step to remove any temporary collections left by a crash
Rename and expand the remit of migraiton 009

- Fix the cappedness of all buckets
Merge pull request #247 from alphagov/set_2weeks_capped_size_2

Increase the size of realtime collections and fix cap size of all others