Fix regression in scroll handling

Before commit de87cab0d2d2 ("Apply some clazzy fixes"), the "scroll"
method was overloaded as signal to set the correct position in the main
view. After that change, this subtle override is gone. The last trace
was removed in commit f136b953f4e3 ("remove broken connects").

Restore the original behavior with renamed signals to avoid confusion.

Reviewed By: mreeves

Differential Revision: https://phabricator.kde.org/D15411