[NEW] Porting wf from lhcb

This is a partial porting of the LHCb "workflow" package to DIRAC. In practice, this means providing a base line for VOs to easily use the "Worfklow" modules, using the "modules" provided.

Only one file changed, all the others are either new or have been deleted. The file that changed is Job.py, specifically the setExecutable() function.

The only module present in DIRAC was the "script" module, that could be found in DIRAC.Core.Workflow. This is now found in DIRAC.Workflow and is an extension of DIRAC.Workflow.ModuleBase.ModuleBase. 2 more modules have been added (one, still under development).

Everything here is extensively tested, with the unit tests that can be found here, and using https://github.com/fstagni/TestDIRAC which is a very first porting from the LHCbTestDirac package (which provides an extensive series of tests for the LHCbDirac certification). This will not affect in any way the other VOs (and probably only ILC is at the moment using the workflow package). Due to these considerations, I pointed this development to DIRAC v6r9, but I am open to discussion on this last point.

I can write some minimal doc if this is accepted for v6r9.