Added QR code with API key on Settings dialog
QR Code generation uses jquery.qrcode and a custom knockout binding

This way it will also be possible to easily add another qrcode to the user api key later. Refused to work for now (value binding doesn't update), so commented out right now, but works in theory.
Added changelog entry for qr code
Merge branch 'imrahil-feature_qr_code' into devel
Merge branch 'devel' of github.com:foosel/OctoPrint into devel
Added a couple of changelog entries for previous commits
GCODE viewer now doesn't stumble over completely extrusionless GCODE files
And some more changelog entries (some day I might actually catch up...)
Encoding has to be specified before any other line of code
Merge branch 'master' into devel
including plugins' main template (='name of the plugin'.jinja2, e.g. cura.jinja2) to index.jinja2