This reverts to the way stable does things. Smooth seeking is nice and
all, but slows things down and doesn't give the instant reponse that
mappers are used to.
This should fix some performance issues regarding seeking as it no
longer tries to render large portions of the map during the seek
operation.
Note that I've also forced the summary timeline to always non-smooth
seek. It was bugging out in weird ways when doing smooth seeks and I
don't want to attempt to fix it.
Bookmarks don't show on real beatmaps, but they do show in test scenes
(namely `TestSceneEditorSummaryTimeline`).
Also does some more changes to adjust the markers to the latest updates
to other markers.
- Use slightly different hue of green to distinguish from difficulty
control points. The colour is still not ideal, but picking
a distinctive enough hue is pretty hard.
- Place the preview time part at the bottom rather at the top.
Not sure why it was at the top; not only could it overlap with the
control points, but it also looked quite badly misaligned there
when bookmarks were displayed at the bottom.