[IMP] Web Warning Sounds

Implementation of Web Warning Sounds module. Please check README.rst file for more details on how it works.
 I think that this is good enough since framework didn't intend and make any easier way to add audio to warning message. As for onchange here also the original method is overwritten and lines 46-52 are added. I'm not sure what you mean though by passing sound field to web client? Since JS Audio API requires only the resource location, I think it is a good approach just to parse that from the warning message and use it to play the audio.