Export svgParabolaPath and svgSinusoid path

Summary: Like svgPath, we want to export these functions via KhanUtil to be used elsewhere.
This will let us update SVG paths that were generated with graphie.parabola or graphie.sinusoid,
rather than remove them from the DOM.

Test Plan: It's Hack Week--make sure I spelled the variable names correctly?

Auditors: aria