a data visualisation dash component in a generic flask app

Derived from the Plot.ly Dash Flask Tutorial - README from that project is at end of this.

Allows a folder of tabular files from sensors to be viewed and subsampled if huge. Experiments with dash and in particular with dash in flask

Fair bit of mucking about required but after realising the futility of keeping any state handy, it seems to work. Data has to be re-read to be re-sampled. Caching needs thought...not sure I care yet.

Source code for the accompanying tutorial found here: https://hackersandslackers.com/gaining-full-control-over-plotly-dash/