Parse media info at ffmpeg web playback

It does 2 things:
* <b>Generalize output text filtering</b>
Lets the launcher of any process parse its output in real time if it wants to. Right now the resume feature is examining all output under the sun looking for ffmpeg  "Duration:" matches, after this ffmpeg video does the parsing for itself.

* <b>Parse web media info at playback</b>
With web streams we're lucky if we know duration beforehand, let alone other media info.  This is a "better late than never" approach so ffmpeg web can create a proper mediainfo object once it sees the header at playback and update the resource and transcode folder accordingly. A couple of things:
   * it changes ```DLNAResource.addChild()``` a bit so resources can be updated, I've had it running for a month or so without seeing any problems, but as always more testing would be good since we have a lot of moving parts these days :).
   * the ffmpeg header parsing code in DLNAMediaInfo is put into a separate function so it can be called independently, but I haven't fixed indentation yet since it just makes the diff unreadable and scary-looking