Processes/hh2bbvv

[mafrahm]

This PR adds the hh2bbvv processes requested in #31 and (hopefully) all relevant subprocesses.

This leads to a total of 104 processes:

• 8 different "main" processes (bbVV, bbVV_sl, bbVV_dl, bbWW, bbWW_sl, bbWW_dl, bbZZ, bbZZ_dl) for both ggf and vbf
• for each "main" ggf process, 4 sub-processes for kl variations --> (4+1)*8=40 ggf processes
• for each "main" vbf process, 7 sub-processes for kl,cv,c2v variations --> (7+1)*8=64 vbf processes

Note that there are no HH (vbf+ggf) processes. We could add them, but I don't think we need them.

The ID scheme is documented in the docstring.

Closes #31