Improved architecture, documentation and flexibility, added working tests for preprocessing of images

See merge request cribe001/dlc_flytracker!7

Added ModuleSettings in skeleton modules, to have module specific settings that can be loaded directly in SkeletonFitting class (in function of which module is used)

Changed the names of the functions of animal module to remove direct mention of type of body part (wings, body_slim, hybrid) + Corrected imports

Small bug fixes for test_batch_multiprocessing_images_preprocessing, can now run multiprocessing successfully

Added possibility to load setting for reconstructor, blob detector and background subtraction from a dictionary

-> Finished debugging test_batch_processing_image_preprocessing

Bug fixes: corrected handling of self.settings.image_ratio, usedd to correct dicrependcy between the size of the images used for the calibration and the ones used in the current analysis

Now using kwargs['camn_to_process'] instead of camn_to_process to be able to save this later and simplify code

Added image_ratio parameters in reconstructor3d

Added find_common_substrings_with_one_separator and find_uncommon_substrings + Use them to compute frame number of images

Get frame numbers from ImageSequence (still missing function that will estimate this from image name (and nb leading zeros)
+ corrected .get_path (was .get_paths()) from ImageSequence