Added Openloops as a new external package.

Downloads all existing processes and compiles them.
- `openloops.cfg` contains gFortran flag needed.
- Compiles with -Os to try reduce the disk / memory footprint of those
  libraries.
Merge pull request #1178 from ktf/openloops

Add openloops external.
Merge remote branch 'origin/IB/CMSSW_7_3_X/stable' into IB/CMSSW_7_0_X/stable