[Feature] Allow downloading multiple files as single zip archive rather than many different downloads

[TheZipCreator]

Is your feature request related to a problem? Please describe.
It's a little annoying to do a conversion then get like 20 download popups that you have to click through.

Describe the solution you'd like
There should be a toggle somewhere to set multi-file downloads as downloading one zip archive containing all of them instead. Where exactly this should be is probably a topic best reserved for #73 (hence why this is an issue and me doing a PR).

[exurd]

I think it would also be important to give the user the option to select the archive format for storing those files.