Make responsive

[Manishearth]

Would be nice if this could work well on a phone, perhaps showing the textbox as part of the lookup/options/etc tabs, with textbox by default; and showing the code points and specific info pane below, both collapsible.

(I might work on this, but it depends. Ideas on how to lay out the page welcome! I may also be doing similar stuff for other tools)

Eventually I'd like to make an offline app out of this and other tools. For personal use, at least, though if you want me to distribute it or would like to do so yourself that would be great too!