[Feature Request] Mass import ROM options

[skamansam]

There is an option in the UI to "Import a ROM that is known to Lutris" which imports a ROM and automatically assigns it to a emulator. You can also do this with multiple ROMs in the UI by dragging and dropping one or more files onto the main window. In order to achieve this on a larger scale, there are two possible options:

1. There should be a way to use the --import option in the CLI that achieves the same as the UI above.
2. Another option in the "Add Game" dialog to mass import a folder, using the same method as importing a single one. Possibly with an option to recurse folders.
3. Allow drag n drop of folders onto the UI, optionally with a dialog or preference to allow recursion.