Rename idempotent subscriber

- [ ] @srobaudo 
- [ ] @gmoskovicz 

The Idempotent concept was entirely too confusing.  We finally came up with better names.  Since you guys are the most familiar with Druq code base besides myself, please let me know if I've missed something.

PPM integration at https://github.com/daptiv/Ppm/pull/2240
I know this will work, but should this be typeof(Migration20140915)?