Session control & manifest writing #108

Currently the concepts of video recording and session are a bit mixed.

It would be useful for a session to have the following capabilities:

• Can contain multiple recordings
• Can have multiple inference recordings / processors related to that as well
• Should propagate a dashboard / context to clearly report current app status to other callers
• Could listen to a socket for triggering the recording directly (i.e. experimenters with a different experimental GUI can make this one the follower instead of the master).
• Each session should write a manifest with the metadata of all recordings that happened. This greatly simplifies the database ingestion and makes it more robust. This includes the metadata from the camera