Main window: Implement log panel

[CmdrDats]

This will be useful, particularly in the early stages, so that testers can quickly send me relevant information when there are problems.

[CmdrDats]

This actually turns out to be surprisingly tricky to get right - the socket.io library uses slf4j and so there's all sorts of bindings involved here with log4j and clojure.tools.logging.. I don't know.. it's a mess, and I'd rather be doing other, more interesting things.