List Themes

[BryanSchuetz]

Was thinking, if we're going to have a bunch of themes—would be good to return a list of them. Something along the lines of :themes list would open a modal (same way :explain does) and list out the currently available themes. Just the name and a short description.

Related: We should probably have close buttons on these modals as well. And, I guess we'd have to figure out what to do if more than one modal was open at a time...let them stack, close the existing one and open the new one, etc.

I've never worked with Mithril.js but I could take a shot at figuring this one out, if we think it makes sense.

[ondreian]

This is a good idea, but we might want to hold off until I can work on the command system more