Improving file handling in sidebar

[rdilip]

Description

I'd like the ability to select and delete multiple files at once from the sidebar. Currently, you can only select one at a time, which makes it a bit difficult to e.g., delete a large number of images.

Use Case

I encounter this issue a lot because I duplicate a project to get the basic formatting over, but then it copies over all the images and I want to delete those. I have to delete them one at a time, which is a bit clunky.

[laurmaedje]

Closing in favor of #272 which is a bit more specific.