BugFix for Lepton Isolation

It was found that the lepton isolation are changed to >1 instead of
<0.4 etc in the samples. This is because the Isolationvar got overwritten in
the IsoTrackFilter module, which calculated the isolation use PV tracks only.

To fix this problem, I add a new variable TrackIsolationVar to the Candidate
class to store the track isolation in the IsoTrackFilter module. However, the
TreeWriter for IsoTrack will still store the TrackIsolationVar into
Isolationvar.
Merge pull request #4 from zhenbinwu/clean

BugFix for Lepton Isolation