Update MCWeighter

So I created a branch "mcweighter-decouple-buildSumwMap" and made two changes:

+ Take out buildSumwMap from the constructor
+ Change defaultLabelBinCounter from "SusyProp Veto" to "Initial" 

The problem was this "SusyProp Veto" is needed only for the simplified model points that need diagram cleaning, but all the rest, i.e. pMSSM, NUHM etc. are fine (they can have SUSY propagators as a part of the model). So using "SusyProp Veto" as the default was giving wrong answer for other signal models (BG is unaffected).

After the changes, the user needs to call buildSumwMap after setting up the correct setLabelBinCounter, i.e.:

_mcWeighter = new MCWeighter(m_tree, xsecDir);

will become:

_mcWeighter = new MCWeighter(m_tree, xsecDir);
if( isSimplifiedModel ) _mcWeighter->setLabelBinCounter("SusyProp Veto");
_mcWeighter->buildSumwMap(m_tree);

for isSimplifiedModel, I don't think we have a built in function. There are very many DSIDs, so that's a bit of a pain to make the call using that information. When I run my jobs, I give the sample a name and I use it to make the judgement.

Should the user not call buildSumwMap, the job will simply abort.