Replaced !-newlines with ¶-newlines

Discussion on LJ consistently disliked the bang-newline approach, so
switched to this suggestion from Darker.

(Also checkpointing changes to Create a Thing.)
You now pick the Model before the Create screen

This will allow us to remove the ugly Model-selection stuff at the top
of that window.
Removed the annoying change-Model UI

This has been bulking up the top of Create/Edit for a long time, and
really bothering me.  For now, I've removed it entirely from the UI;
later, we should re-add a way to change the Model, but it's a minor edge
case and better removed for now.