[FIX] userprefs: Untangle mess of having two forms with the same submit action, which meant saving the info tab reset the prefs, and saving prefs tab reset the info. No idea how it got so bad but it was a while ago... at least before in 18.x (hopefully will address wishes 7249 and 6758, thanks hman)

(cherry picked from commit 431eb781 with some manual fixes)