boolean edit_mode_ instead of current_mode_

sort of working now, all kinds of horrible formatting issues though
fix some sizing issues
fix more heights & set code background white
match code size with editing size, and various other fixes

except for the varying gutter (argh!), edit pos is the same
set hljs class automatically
fix read only bug
fix initial language
update code on change
reset result consistently
fix gutter width and match it with code padding

edit now perfectly matches code
still needs cursor position on click (if we're keeping click-to-edit)