Create-InSAR-Stack functionality

 - 2 ways for computing prelim offset for stacking: ORBITS and GCP
 - UI and Graph adapted
 - not used functionality removed (eg, extent, resampling)
 - code cleanup

ORBIT method: purely based on orbits and timing metadata - no GCPs, nor
any other annotation used.
Coarse and Fine Coregistration functionality

 - operator
 - core utils
 - UI