Update build task to overwrite nodewebkit.options.platforms array.
Initial config array is overwritten with an array of platforms as detected by parseBuildPlatforms.
Update README to reflect platform names as understood by grunt-node-webkit-builder.
grunt-node-webkit-builder doesn't understand `mac`.
Add git rev to about dialog
Merge pull request #210 from OnAzureWings/specify_release_build_platforms

Fix specifying build targets
Add default OSX Preferences menu item and key binding
Only trigger Settings from OSX Preferences menu item or key shortcut if there is not already an open dialog box
Merge pull request #223 from brandonhamilton/master

Add default OSX Preferences menu item and key binding