FIREBREATH-236 & FIREBREATH-237 Patch

This patch solves a bug on SimpleStreamHelper::SynchronousRequest( ) and adds some new features on SimpleStreams. Namely:

1. Adds a **HttpProgressCallback** that can be registered using ```BrowserStreamRequest::setProgressCallback( )``` in order to receive feedback regarding the download progress.
2. Adds a **HttpChunkCallback** that can be registered on the ```BrowserStreamRequest::setChunkCallback( )``` in order to implement a custom data receiving function.
3. Adds a **HttpCompletedCallback** that can be registered on the ```BrowserStreamRequest::setCompletedCallback( )``` in order forward the notification of download completion.

The **HttpProgressCallback** can even be used with the classic **HttpCallback** interface.