CFS_v2: fail gracefully if no sky options given

 -before, failed only deeply in InitDopplerSkyScan()
 -now already fail on input consistency check
 -Alpha, Delta still have nominal defaults of 0.0, but will fail unless given by user
 -refs #942
ComputeFstat: added santiy check to catch invalid single-SFT input

- throw an explicit error in case of single-SFT input in any detector to
  avoid returning singular results
- fixes #1059