add capped collections

[tacaswell]

As discussed with @arkilic capped collections provide an easy way to essentially monitor a collection via a tailable cursor. The capped collections should be added to by all of the insert operations.

• [ ] add code to make sure that parallel capped collections exist for start, stop, descriptor
• [ ] add code to insert into the parallel capped collection
• [ ] write example monitor scripts

[ghost]

We should have a short discussion about the size of capped collections, what the api for monitor routines looks like, and possibility to replace the existing caching layer with capped collection(since higher throughput).