Add gg_tt01g.mad to the repo, including Stefan's P1/P2 fixes

[valassi]

Looking at @roiser 's MR #620, this includes also a few fixes for processes with P1 and P2 directories.

I am merging them here, and applying them to gg_tt01g.mad, which this time I am adding permanently to the repo.

[valassi]

CI tests are ok, I am self merging

Note, there are now 7 processes sa and 7 processes mad in the repo

[roiser]

Hi @valassi just to mention the "real" process they are looking for is 0,1,2 and 3 gluons in the final state. We may want to add this aswell.

[valassi]

Hi @roiser, thanks. Yes I agree at some point we should add and try the "real" processes of ATLAS and CMS. Here my point was just to have in the repo a simpler and more manageable provcess, which however has some of the complications of ATLAS/CMS. In particular non of pur previous gg_tt... gg_ttggg alone had separate P1 and P2 directories (which have their own nwf, npar etc... issues). So I added this for the moment and I will try to regenerate it each time (I should also add it to build/runtime tests....)