Handle run2 in B2DXFitters

Hi @adudziak,

I created a branch called B2DXFitters_run2 to start implementing the handling of run 2. So far I updated all the relevant functions in GeneralUtils: c11d2093 I implemented things in such a way:

• merge=year/both, year=run1 are still valid for backward compatibility.
• merge=yearrun1/yearrun2/yearall/bothrun1/bothrun2/bothall, year=run2/all are now also possible. I hope that you like this implementation.

There is only one thing left, I think: the "GetDataSet" function in GeneralUtils. This would require some care since it's more tricky.