Add cgminer, crypto currency mining application and all relevant dependecies

This pull request is updated and rewritten #452 pull request, which is now closed in honor of this pull request.

Packages introduced here:
- amdapp-sdk, amd opencl sdk
- amdadl-sdk, amd display library, for gpu statistics
- cgminer, crypto currency mining application

These packages are tested on my mining rig deployed with nixops. I'm running this for about few months and all relevant bugs have been patched.