shell: sidebar-thumbnails: move scale-factor signal to the sidebar widget
The signal handler should be registered to the sidebar widget itself, instead of the box. One consequence of this is that the callback signature does not match the registered handler's one.
Fixes: bc717db9 ("shell: make PpsSidebarPage an abstract class") Closes: #203 (closed)
Note: I do not experience that bug.
Edited by Markus Göllnitz