added node-webkit to generate standalone app.
Merge remote-tracking branch 'upstream/master'
Make desktop app directory with all nedded files before build it.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	Gruntfile.js
Setup nw releases destinations to build folder.
change node webkit versions to work with older node versions.
Fix : Duplicate Current Frame bug (shift+n)

Events were not raised when using Duplicate current frame on
PublicPiskelController.
Change node webkit releases location, ignore unecessary files.
Merge branch 'master' of https://github.com/juliandescottes/piskel
Merge pull request #178 from fsvieira/master

Standalone App with node-webkit
Merge branch 'master' into feature-dynamic-palette