Improve following of SLHA standards

[ChrisJChang]

Found when interfacing smoking to gambit. We should add more information to the MODSEL blocks. Currently only add a single entry.

I have tried adding the 6 block, but currently this causes pythia to fail to initialise.

[ahye]

I'm trying to reproduce this, but I don't have the exact SLHA file you guys were using to test this. Could you send this @ChrisJChang or attach it here?

From just browsing the code the problem seems to potentially be that pythia (for unknown reasons) requires the VCKMIN block to be present whenever there is FLV in the quark sector.

[ChrisJChang]

ColliderBit.log

I have attached the ColliderBit log that spits out the SLHA for my test. You cna see that this does contain the VCKMIN block.

A little testing with extra pythia verbosity seemed to suggest to me "Warning: lepton FLV on but UPMNSIN not found", however the UPMNSIN entry is present in the SLHA. I was a bit confused because in pythia's SusyLesHouches.cc file (around line 1500ish), it raises this from the check: "if (!upmns.exists())", but there is a separate upmnsin object, so I was not sure if the check was referencing the wrong object, or whether we should have the UPMNS block in the slha.