Save H264 video to disk

In order to support our future goals of providing users Video on Demand of previous streams, and Clips of particular sections of a live stream, we need to know how to save H264 to disk in a playable way.

My theory is that we could easily do this in a way similar to how Peer Snap works (and based on the architecture we come up with in https://github.com/Glimesh/waveguide/issues/7). Since we'll be able to consume the RTP packets, and save them directly to disk.

Some Pion examples:
* https://github.com/pion/example-webrtc-applications/blob/master/save-to-webm/main.go
* https://github.com/pion/webrtc/blob/master/examples/save-to-disk/main.go
* https://github.com/pion/webrtc/blob/master/pkg/media/h264writer/h264writer.go

Start by reviewing the architecture proposed in issue #7 and the linked Pion save-to-WebM, save-to-disk, and h264writer examples. Determine how RTP packets will be consumed and persisted; done means H264 video is saved to disk in a playable form for future video-on-demand and clip support.

Written by the indexing model from the issue text.