Use separate templates and widgets for all HTML

[kltm]

There should no HTML in App.js--everything display should be through a widget or an API.
Need to simplify codebase and enforce separation.

[kltm]

This should be pretty much done--all dialogs/pop-ups are now self-destructing shields. There are a few remainders, like cursors and some types of message passing, but I think they should mostly work out when we bring in the moderator and restructure things a bit more sanely (i.e. #14 ).