Ability to edit SVG code within menu

[lacymorrow]

From a comment by @rknDA1337:

a custom code box for advanced users. Being able to edit the SVG's code themselves (without breaking them; perhaps only allow saving them as a copy/with new name - if it was edited) is enough to both allow custom styling and any other changes an advanced user would like to make. (Also, the below-mentioned SVG-parse-check should give the go-ahead when saving/before saving) In addition, perhaps this 'advanced' setting could allow you to simply paste your own SVG.