add Forward boolean to Jet DataFormat

@mulhearn @jimbrooke @kalanand @apana 
Stage1Layer2 would like to change our jet finder to make sure that central jets have no HF energy. This means that we need to deal with the possibility of two jets at the same eta-phi position, one including HF (a forward jet) and one not including HF (a central jet). 

I think the simplest method for handling this extra required info in our algos is to add a forward member to the l1t::Jet class, which I have done here. This is build and run-tested. Previous uses of the constructor should still be fine.

Is there any reason not to merge this? I had to edit classes_def.xml, wasn't sure what the procedure with that was.

Thanks,
Alex