Add FileOperationsPlugin

[mkalinski]

Check-list

• There is a linked issue discussing the motivations for this feature or bugfix: Improve docs around DnD to copy files and rename to move #3549
• Unit tests have been added where possible
• I've added / updated documentation for any user-facing features: individual plugins don't seem to have a dedicated documentation section
• Performance seems to be comparable or better than current master

What this change is adding / fixing

This change is adding a songsmenu plugin that provides two menu options: Copy and Move.

These options open a file chooser to select destination, and then copy or move the selected songs to the destination.

Moving / copying is done in a separate thread.

A window is opened with a progress bar, log of each file copied / moved and any exceptions that might occur, and a button to abort the copy / move.

[declension]

Did you try doing via Custom Commands ? It seems like it should be doable

[mkalinski]

@declension It's technically doable via Custom Commands but it's cumbersome. The destination can only be passed as parameter, which needs to be manually typed as text input every time.

There are good alternatives to this plugin proposed in #3549 though.

[declension]

Closing in favour of #3459