On refreshing the FMs list when new ones are added

[FenPhoenix]

People sometimes ask if the FMs list can be refreshed to include newly added FMs on disk without restarting AngelLoader, or confuse "refresh" / "refresh from disk" / "scan". We should try to improve this situation.

We should make it clearer / more obvious that there is such a feature, but other possible ideas to alleviate the situation might be:

• [x] Allow dragging new FMs onto the window and have AngelLoader add them to your FM folder(s) (asking which folder to add to if there are multiple)
• [ ] Allow adding an option to right-click menu on zip/7z files "Add to AngelLoader"
• [ ] Add option to watch for new FMs in the specified folder and pull them in automatically
• [ ] Just go all the way and allow downloading new ones right from the UI