"Loading <sample name>" message should show progress

[maks]

Leading on from #144 especially for large samples, not showing any kind of progress indicator is frustrating as you have no idea how long the sample import/load will take. Even a basic count of bytes read/bytes total or even better some sort of animated ascii widget would be great here.

[democloid]

this is going to be very hard really. That routine is single threaded and with interrupts disabled, so not much that could be done, unless we updated the UI directly from the routine, but that would mean having a lot of code that needs to be loaded in RAM.

[maks]

Actually, maybe by fluke, but it actually works!
I'll put up a PR shortly to get your feedback on if the code is ok or not 🙂