Support multiple selected rows

[datatags]

Summary

As briefly mentioned in discord, I thought it'd be useful to be able to select multiple rows with the standard methods (Ctrl+Click, Shift+Click, Ctrl+A, etc.) and for it to only prompt you to add updates/DLC once. This PR adds this.

Notes:

• I'm not super experienced in C++, so if something needs to be adjusted, let me know.
• When no rows are selected, the "Add to queue" button is disabled.
• When some selected rows are in the queue and some are not, pressing the button will add all selected items to queue. Items that were already in the queue remain in the queue.
  • Consequently, the "Remove from queue" button is only displayed when all selected items are already in the queue.
• I think I've tested the changes pretty thoroughly and it seems to behave as I'd expect. Not to say you shouldn't test as well, of course 😉
• I've also added a script, build_windows.sh that I used when testing. (It's adapted from the GitHub Actions script.) I used it with MSYS2 MinGW x64 but it may work with other environments as well.

[Xpl0itU]

As I said in the discord, could you remove the build_windows.sh script? It’s not even building but rather deploying, to build and execute it you can do it from the mingw shell itself

[datatags]

Thanks, sorry I didn't get back to you very soon, I submitted this and went to sleep shortly after

[Xpl0itU]

No worries, I had write access to your fork so I handled that myself