Lots of bug fixes and improvements for mobile devices

[makermelissa]

Depends on adafruit/ble-file-transfer-js#5.

Here's some features of the new features:

• Works with the following fix: Split listdir entries across two packets adafruit/circuitpython#5524.
• Works on mobile devices without crashing.
• Height adjustment fix for mobile devices
• Improved color scheme so it's actually readable.
• Connect no longer tries to bond, making reconnecting much simpler.
• Busy indicator during bluetooth transactions.
• Better Error Handling.
• Mobile Menu items are now fixed
• Disconnect button works properly on mobile
• When opening another file or starting a new document and the current file isn't saved, you now get a choice of saving, discarding, or cancelling.
• Minor bug fixes related to the file dialog.

[tannewt]

Looks good to me! Thanks for polishing things up.

[makermelissa]

Ok, it's passing now. I don't have merge rights on here, so you'll have to do it.