Add batch upload popup

[kidneyhex]

Link: https://kidneyhex.github.io/EspruinoWebIDE/

An updated file upload. Just providing to save you time, if it helps. Take as much or none of it as you'd like. :)

• Single files act the same as before.
• Multiple files give a window listing them all with rename options.
• Image/audio files get a "Convert" button that's required before upload. They show "pending" in red until the conversion has been set up, then "ready" in green.
• Multiple files with the same "target name" give an error about the duplicate name.

(No special logic for metadata.json or apps, just the existing image/audio conversion.)

The status window is a little weird. The first file has a normal message and progress bar, then each file after that ends up getting its status messed up by the previous file's "Sent" status.

[gfwilliams]

Ok, thanks! there are some massive changes here though - I'll have to wait until the new year before I can really look at them - and also test to make sure they still work ok on SD cards.

It would be good if you could try and look into the status issue - I don't feel great about merging something that we actually know has issues - especially as it could be trying to send over a new file while the last one is in progress.

I did take a quick look at the code though and it looks ok - maybe changing uploadNext(); to be setTimeout(uploadNext, 0); is enough if it's not a deeper issue?

One thing I did spot - it looks like maybe if you upload a wav/image/etc file it actually forces you to convert it before it'll upload? Previously you could upload a file without having to convert it - and there are cases (like developing for the Pip-boy) where you'd want to be able to upload a Wav file without conversion