"Scanning failed: Illegal access" - make more aesthetic

[HexTree]

The Alert box which pops up when you deny camera access is kind of technical, we should instead give a message to the user that they should Allow if they want to scan points.

[sayyari]

The proper messages are actually ready to use but they were going to show as text under the button. I'll fix them, they're in the scan.js.

Thanks for hunting.

[sayyari]

Added but yet to test a dialog of error instead of a debugging alert.