plugin XEP-0264: updated size to get values closest to standard one:

- sizes used for thumbnails are now matching common resolutions.
- added BIG and FULL_SCREEN sizes
- sort thumbnails by sizes when parsing them.

sat/plugins/plugin_comp_file_sharing_management.py

@@ -404,7 +404,7 @@ class FileSharingManagement(object):
             if media_type == 'image':
                 thumbnails = []
 
-                for max_thumb_size in (self._t.SIZE_SMALL, self._t.SIZE_MEDIUM):
+                for max_thumb_size in self._t.SIZES:
                     try:
                         thumb_size, thumb_id = yield self._t.generateThumbnail(
                             file_path,