CRB: OpenCL
- Externalized CL commands (To be merged in Harts)
- Fixed bugs in cl source code (bad access patterns)
- Fixed correct use of cl kernels (instead of hardcoded path to source
  code)
- added option to be able to select either cpu or gpu for CL
  implementation
- Added output debugging code
- Lots of other bug fixes and dead code removal
Merge branch 'develop' of https://github.com/feelpp/feelpp into develop