- replaced misuse of "FileLoadException" with a custom LoaderException to handle file loading issues with better continue/fail logic
- removed "Save As" and replaced it with "Convert list" menu item that shows information on how to use a reference list instead of direct conversion
- added round-trip unit test for all loaders to check reordering channels and favorites, saving and reloading
- internal code clean-up regarding different favorite list modes (none vs. flags vs. ordered per source vs. mixed source)
- fixed handling of reference lists (matching sat/cable/antenna, digital/analog, tv/radio/data criteria), especially for m3u lists which don't contain ONID-TSID-SID to identify channels