The timer used to time out and invoke Viewer::informationSwitch() twice
before getting destroyed. This caused the following bug:
1. Press 'I' to Show Info in YACReader.
2. Restart YACReader (exit and run again). Info is visible.
3. Restart YACReader one more time. Info is hidden.
Apparently, when informationSwitch() was called a second time soon after
the first one, informationLabel didn't hide for some reason, but the
wrong value (false) was stored at the SHOW_INFO key in Configuration.
Without this commit the horizontal wheel on a two-wheel mouse acts the
same as the vertical wheel in YACReader.
horizontalScroller is used analogously to verticalScroller in
Viewer::scrollTo(). So I made the horizontal wheel work analogously to
the vertical wheel except for moving to the next or previous page.
