Background Job for Collecting Operation Counters

Create background job that collects all the status stats and info about each MongoDB node in the replica set and stores that information in a capped collection in "mongo-tools".

The job could poll the database every 20 secs or so and it store something like this each time:

```javascript
{
  node: 'host:port',
  ops: {
    updates: xx,
    inserts: xx,
    deletes: xx,
  },
  connections: xxx,
  cursors: xxx,
  ts: ISODate('...')
}
```

It would effectively just record the node, counts for all ops and a timestamp for when the info was recorded and stash this in a collection without our own "mongo-tools" database.﻿

Requirements:
- [x] Collection of all operation types on a configurable interval.
- [ ] Support for single MongoDB instances, replica sets and sharded clusters.
- [x] Configuration (YAML) for storing settings for which nodes to monitor, the polling interval and capped collection size.
- [x] Common Ruby API for using this data throughout the tool suite.
- [ ] Feature Documentation on the Wiki.

Depended on By:
- #40 Database Visualizer
- #39 Database Explorer
- #41 Alerts & Monitoring