Generate figures on the fly rather than storing them

[GiudGiud]

Feature Description

Results figures can be generated while building the documentation This could reduce the storage needs of the VTB AND makes sure figures and reference files are in sync

It is easy to update reference files while working on a change, but forgetting to update the doco because of just forgetting or because you dont have the plotting scripts handy to do it

Design

Use and maintain plotting scripts for figures

Impact

More up to date doco