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

*Update the cap size of realtime collections*
They should be capped at 4mb which gives us about 2 weeks worth of data
Some are not capped, some are capped. This migration involves creating a new collection, capped to the correct size and then copying the data across.

*Fix cap size of all collections*
No collections other than realtime collections should be capped. This migration makes them uncapped.

This pull request supersedes #242