Fixed the rendering of the tact numbers in the timeline widget. Before
this fix they were not readable because they were too big. Interestingly
in this case the fix is to use a font size in pixels (half the height of
the widget). The numbers are now also rendered a bit darker than the
lines.
Also removed the pixmap for the timeline from the code and from the
filesystem. It was only used to determine the fixed height of the widget
but not rendered. Therefore it was removed and the height is now
directly set to 18 pixels which was the height of the pixmap.
