Move KMBM variable out of KV member in keyboards to match compiler behaviour

Fixup attachType for web debugger in Keyman Developer

Addresses the recent iOS image asset requirement change.

Removes the 'free' set of asset images and attaches the newly required 'marketing' 1024x1024 icon.  Addresses #371.

Refactor longpress logic so key text is not confused with key code

`String.fromCharCode()` has a limitation to Unicode characters in the BMP. Change to `String.kmwFromCharCode()` to handle entire Unicode range.

Also clarified how default key codepoints are processed.

KeyboardHarness changes:
- Change text area font on keyboard change
- Added U_10481 to test longpress keyboard.
- Remove test tchad keyboard

Update comments explaning how control codes U_0000 to U_001F and U_0080 to U_009F are suppressed.

Also updated longpress test keyboard to test control codes.