CYCLUS_DEBUG_DRE for extra info dump when running simulations

Just set CYCLUS_DEBUG_DRE=1 in your environment when running cyclus to create
tables for information on all request and bids during a simulation in the
database.
I decided that the manager class was best because:

* it resides at the top of the resource exchange control flow - and so is only allocated once per simulation rather than every timestep
* It is a smaller class with simpler code/control-flow and so the debug code just seemed to fit in better.