A lot of changes after detector review:

A lot of changes after detector review:

* AliFMDBaseDigit (and AliFMDDigit and AliFMDSDigit
  by extension) derive from silly AliDigit.
* Up to 3 track labels propegated from hits to
  digits and sdigits.
* Implemented AliFMD::Raw2SDigits (see also
  scripts/TestRaw2SDigits.C).
* Added survey data of FMD1 and 2.
* Added FMD2 survey markers to geomtry.
* Survey to alignment is almost done.  The code
  is in AliFMDSurveyToAlignObjs.  Note, FMD2
  survey can only give FMD2 z-offset, while FMD1
  survey can in priniple also give x,y offsets
  as well as rotations.  FMD2 z-offset is determined
  as a best-fit of a plane to the available data.
* FMD2 and 3 are still roughly 4mm off from design. I
  need to talk to ITS people about this.