change all text UI to be implemented in terms of twisted.conch.insults.widgets

[glyph]

This would be much more testable because we could assert things about each of the widgets doing their job rather than just looking at whole-terminal properties.

Maybe depend on https://github.com/exarkun/invective/ for a little while to get a good text input widget with history, at least until https://github.com/exarkun/invective/issues/4 is resolved.