added tie point filtering by measuring SSIM improvement; fastened grid initialization

components.CoReg.imParams:
- added attribute 'xygrid_specs'

components.CoReg.COREG:
- added attributes 'ssim_orig', 'ssim_deshifted', '_ssim_improved' and property 'ssim_improved'
- _get_opt_winpos_winsize(): outlier assertion is now a tracked exception
- _get_image_windows_to_match(): bugfix for passing rspAlg from wrong attribute
- added function _get_deshifted_otherWin()
- added function _validate_ssim_improvement()
- calculate_spatial_shifts() added call for _validate_ssim_improvement()
- added function _get_inverted_coreg_info()

components.CoReg_local.COREG_LOCAL:
- implemented keyword 'tieP_filter_level'
- view_CoRegPoints(): implemented keyword 'hide_filtered'

components.DeShifter.DESHIFTER:
- bugfix for not handling attribute 'band2process' correctly
- added attributes init_args and init_kwargs
- revised _get_out_extent(): bugfix for not handling clip extent correctly; bugfix for wrong call of find_nearest()
- correct_shifts(): bugfix for wrong condition in connection with target_xyGrid keyword

components.Geom_Quality_Grid.Geom_Quality_Grid:
- implemented keyword 'tieP_filter_level'
- get_CoRegPoints_table():
     - exclusion of points outside of overlap polygon is now much faster
     - added new columns to CoRegPoints_table: 'SSIM_BEFORE', 'SSIM_AFTER', 'SSIM_IMPROVED', 'LAST_ERR'

- updated __version__