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.
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-tiled-preview