stgc calcs: revert names; move generic sector calcs to separate file

Details:
- stgc.Pos: revert the branch names to the ones for HitDumper (will
  define a similar calc for the new TDS tree, rather than polluting
  this one)
- move the generic calcs IndicesOddSector, IndicesEvenSector to
  separate a file (sector.py)
add sector.py, updade __init__
add tds.Indices (needed to make inclusive xy plot)
work in progress, now plot inclusive xy map