Add Icon component

[tchock]

Using icons currently is a bit of a mess. Some places enforce the right size, but using icons standalone often needs configuration (depending on the iconset).

This new Icon component helps with this. It forces the right sizes and also makes it easy to color the icons.

It should have the following props:

prop	type	description
size	'small' | 'medium' | 'large'	Enforces themewide sizes to the icon
color	string	Path to color to use for the icon, default common.black
icon	ReactNode | ReactElement	Icon component or element of icon component