Fix-up graphics to support more output types for snpfreqplot at ORG

toolshed.g2.bx.psu.edu/repos/iuc/snpfreqplot/snpfreqplot/1.0+galaxy3

Test histories. Note that while not failed, some graphic types do not have the sample, file, and other metadata rendered correctly. Getting SVG corrected is probably the most important (for publications).

* **PDF** (only) https://usegalaxy.org/u/jen-galaxyproject/h/test-variant-frequency-plot
* **PDF**, **PNG**, **SVG**, and **JPEG** are ok https://usegalaxy.eu/u/jenj/h/test-variant-frequency-plot

Reported at https://help.galaxyproject.org/t/rendering-svg-from-galaxy/10724. Thanks!

Start with the snpfreqplot 1.0+galaxy3 tool and the linked test histories, then compare PDF, PNG, SVG, and JPEG rendering, focusing on missing sample, file, and other metadata. Use the linked Galaxy Help report for reproduction context; done means the output graphics, especially SVG, render the metadata correctly.

Written by the indexing model from the issue text.