New features and performance improvements

Features:

• Create collages ordered by rows (as before), columns, or as nested sub-collages
• Control image ordering (input order, random, date ascending, date descending)
• Apply image corner rounding and/or collage corner rounding
• Redesigned user interface for Pythonista version
• Separate native Siri Shortcut with all the same features (that runs at about 1% the speed of the Python versions)
• Image/collage size options now determine maximum longest edge, instead of specifying separate width/height

Performance improvements:

• Multithreaded image loading and operations for massive speedup