prepare end-to-end workflows for workshop

[breezykermo]

We want to be able to demonstrate mtriage in a ready-made way with approximately 5 pre-retrieved, pre-analysed workflows.

The majority of these will be demonstrating mtriage's capacity in computer vision (e.g. youtube -> frames -> keras-pretrained/yolov3 -> classified-youtube), but at least one should demonstrate mtriage's capacity in other modes of analysis, e.g. audio.

These can become community examples after the workshop.