Additional Retina support

* Include Icon@2x for plugin icons
* Change Plugin view to 44x44 pixels, to match icon sizes
  so there is no rescaling
Retina support for sticky notes

* fix view-scale bug which caused hit-testing issues
New assets
Merge remote-tracking branch 'apportable/develop' into retina
Merge pull request #1230 from stuartcarnie/retina

Retina