SLCImage now computes approxRadarCentreOriginal when .res files parsed

 - approximation based on half size of dataWindow
Update and refactoring of MasterSelection: interface to height ambiguity and fDC

 - computation, fields, getters and setters for height ambiguity and fDC
 - light refactoring
 - path in unit test fixed

Known issues: The model for coherence computation is not reliable in situations
 like ERS/Envisat cross interferometry. It will underestimate coherence, because
 the baseline needed for the wave-number shift is close to critical (~2km). For
 applications like these a more robust model, that includes principles wave-number
 shift shall be used, or simply the critical perpendicular can be recomputed in
 case of ERS/Envisat interferometry.

Note: needs non-zero values for reference point in estimation, works most
 reliably approx center of scene. If no reference point, the class will
 initialize on (0,0) that can trigger some numerical instabilities in Baseline
 class. It will work on reference 0,0 but estimation can shoot-off a bit.
InSAR Stack Overview now lists info on: Height Ambg and Doppler Centroid
InSAR Stack Overview help reorganized, and update for notes and known issues
Semi-fix for 'external-DEM' in SubtRefDem operator (only partially addresses issue)

 - help also updated listing limitations in handling external DEM
Clarification of 'known-issues' of SubtRefDem in operator help