implemented shifts vector length and angle directly into CoReg; calculation of geometric quality grid now 100% faster

COREG:
- __init__(): added new attributes 'vec_length_map' and 'vec_angle_deg'
- _get_image_windows_to_match(): bugfix for running warp_ndarray in multiprocessing if multiprocessing is disabled
- calculate_spatial_shifts(): moved calculation of X/Y shifts in map units here; implemented calculation of shifts vector length and angle

DESHIFTER:
- __init__(): added attribute 'GeoArray_shifted'
- deshift_results(): added keys 'updated geotransform' and 'GeoArray_shifted' to returned dict

Geom_Quality_Grid:
- _get_spatial_shifts(): now returns values for all columns of quality grid
- revised get_quality_grid(): now much simpler and 100% faster
- view_results() added functionality for saving the output figure to disk