Set the colour of the ruler hover marker to the correct palette colour
Integrated signal handler from qpdfview
Adjusted SignalHandler style to match the rest of PulseView
Corrected label layout when text is empty
Revert "View: Decouple horizontal scrolling from the scoll bar"

This reverts commit 149e359e48ede480f3734cfc5c04bd1399d0d4be.

The original commit fixed the scrolling jitter at high zoom, but
breaks scrollbar paging behaviour.
Ignore H-scroll events while scrollbar is begin updated.

This is an alternative approach to resolving bug 7.
Fixed the H-scroll page width to half a screen rather than a full screen.