SusyNtTools: refactor JVF requirement

Refactor isCentralLightJet and isSignalJet, moving the common lines
to a static function SusyNtTools::jetPassesJvfRequirement.
Verified that the outpout of `Susy2LepCF` is the same as before.
However, there is one detail that I should check with Steve:
`isCentralLightJet` used to have a fabs(jvf), which I don't understand.
In particular, if I add it to `jetPassesJvfRequirement`, there are a
handful of extra jets for which jvf==-1.0.
jetPassesJvfRequirement : require jvfTool only when we need it
add jvfTool as an argument, and revert a few funtions to being static

revert getMetRel, isCentralLightJet, etc. to being static; this is
mostly to avoid depeneding on the datamembers of SusyNt (trying to
make things more explicit, and delegate stuff from SusyNt to smaller
classes).
Note: some of the 2Lep functions are not static yet...todo.
jetPassesJvfRequirement: clarify that JVF can be applied only below some pt
whitespace around ostream operators

Although I don't think it makes the code more readable :-)
jetPassesJvfRequirement: add special case for 2lep analysis

The 2 lep analysis also accepts considers signal jets those that have
jvf=-1. This commit implements the special case mentioned in 6f89095
simplify isSignalJet2Lep, use correct(?) eta/pt thresholds in isCentralLightJet
Merge pull request #2 from gerbaudo/jvf-static

Jvf static