CB-4153 Add --src & --link to cordova create.

Both --src and --source are accepted.
The path is passed via the lib.www.uri of the configuration object
that is later written to .cordova/config.json.

Cordova will keep going into child www folder(s) of the provided path.
Add a check to config_parser that root tag is <widget>.
Remove dead code
CB-5397 Make iOS project file's www/ and config.xml point at the non-platforms versions.

This will hopefully make it easier to use Xcode with CLI.