1. Separated the "starter models" and "more models" sections. This
gives us room to list all installed diffuserse models, not just
those that are on the starter list.
2. Support mouse-based paste into the textboxes with either middle
or right mouse buttons.
3. Support terminal-style cursor movement:
^A to move to beginning of line
^E to move to end of line
^K kill text to right and put in killring
^Y yank text back
4. Internal code cleanup.
