CB-2606 Icons support for iOS, Android, BB10, WP8, Win8, FxOS

Based on original version and PR made by @AxelNennker: https://github.com/apache/cordova-cli/pull/126

The following platforms are supported: iOS, Android, BB10, WP8, Win8, FxOS
Updated documentation can be found here: https://github.com/apache/cordova-docs/pull/201/files
Sample configuration file: https://gist.github.com/sgrebnov/9949313