2D Graphics support

[sn6uv]

Support for graphics is not currently implemented.

[sn6uv]

Recently made some progress towards this:

Note the missing plot axes (not affecting in chrome) - see below.

Previously the svg was generated incompletely on the backend and then finalised with javascript. The reason for this seems to be that we want to include text (and equations) within svg images, but we also want to have svg images within mathml code (e.g. a table of images). That is, MathML[SVG[MathML]].

Firefox in particular has some issues but the problem is more general, see mathjax/MathJax#896. Chrome uses a built-in render (e.g. to label the axes).

The better solution might be to just send the existing js solution (in mathics.js) to the frontend.