an attempt at putting the prompt back with the cells

not a very good attempt!
Merge branch 'develop' into retie-prompt

Conflicts:
	htdocs/css/main.css
	htdocs/main.html
get tied prompt working again

css
- make main-div a strict container of the others to eliminate all
sizing nonsense
- cell area now a comprehensible 100% x 100%
- some crazy thing about output margin-left that i don't understand

prompt
- get the right fudge factor for prompt height
- scroll to end with no animation on any change to the prompt (including history)
don't split at beginning or end of cell; disable split button in result mode

fixes #495