Add alternate version of img2musicXML (temporarily)
Add alternate version of img2musicXML (temporarily)

Changes:
 * Minify page and remove external requests
 * Change image view to be a toggleable widget
 * Replace all "let"s with "var"s (for older browser compatibility)
 * Alert when an non-image file can't be added, instead of silently logging to the console

The purpose of this alternate version is to be used with QtWeb in computers with very low memory, basically.

feikname/img2musicXML,feikname/img2musicXML