Display division motion in textarea without erroneous indentation

We do this by convert newlines into HTML entity newlines so that it
displays in a textarea correctly.

Fixes #172
Redirect to the division page if there's no redirect set

This seems to happen when you're not logged in, you click edit, you
log in and then edit the motion.
Match the (pretty shitty) PHP behaviour when saving

Also covers the scenario without redirects via the `rr` parameter