Add more output formats for images outputs #26
Description
Add options to export output graphs as PNG/SVG.
Avoids issue of the HTML files fetching the Bokeh JS library, they only work offline if that JS library is present in cache.
Issues:
Sizing can be unreliable ( https://docs.bokeh.org/en/2.4.2/docs/user_guide/export.html )
Don't have alternative method to identify intervals in QC process, will have to leave most plots as HTML