Format all JS files and some fixes

- all JS formatted by jsbeautifier
- new grunt task "grunt format" to format all JS files automatically
- due to a bug in grunt/usemin/imagemin, it is currently impossible to add a revision number to images --> shouldn't be a big deal as we are probably not going to change the existing images
- remove reference to not existing vendor.css from index.html
- fix problems identified by jshint for gestures.js and enable strict mode for this file