Add class property

[luluvia]

Resolves #6 by adding a class prop to the icons that allows styling, such as with TailwindCSS. For the actual changes, please consult the build.js and icon.d.ts files. The actual changes consist of adding the class prop to the SVG attributes, allowing the fill color to be overwritten by the class style, and adding the class as a valid prop in the TS definition.

[dsm-72]

Can we get a bump on this?

[dsm-72]

@ramiroaisen