Sending multiple files requires round-trips through file picker

[hmmwhatsthisdo]

When sending multiple files through crocgui, I have to individually pick files one at a time, then re-open the file picker to grab another file. This can be a hassle if trying to send lots of small files in the same folder.

My phone is running LineageOS 16.0/Android 9 - to my knowledge, most of the gallery/file-picker APIs on newer API levels support multiple selections if the picker-intent is called with options to allow multiple selections.

[howeyc]

I'll look into possibly selecting multiple files at once.