Modify THcDC, THcDriftChamberPlane

THcDriftChamberPlane

  1) Remove subtraction of hodoscope starttime from ProcessHits
    which is called by THcDC::Decode.
  The hodoscope start time is determined in hodoscope Decode
   which is called after THcDC::Decode. So drift chamber
   was using the starttime from the previous event.

   2) Create method SubtractStartTime which is called by THcDC:CoarseTrack

THcDriftChamber
    1) Move fChambers[ic]->ProcessHits() to CoarseTrack
    2) Before looping through fChambers[ic]->ProcessHits() in CoarseTrack
        loop through all planes and call fPlanes[ip]->SubtractStartTime()