add a feature to support multiple resource directories

change `app.resources_dir' to accept an Array too, like:

    app.resources_dir = ["resources", "vendor/GoogleMaps.framework/Resources"]
fix variable name
fix a bug which cannot build an app when `app. xcode_dir' contains spaces

RM-40 Can't build with spaces in xcode.app path
`app.resources_dir' will be deprecated
fix a bug which does not launch iOS simulator when `app.xcode_dir' is specified a path other than the '/Applications' folder