The editor clock, which is responsible for performing the seek, was not
aware of changes in control points due to reading from the wrong
beatmap. `loadableBeatmap` is not actually changed by any of the editor
components; `playableBeatmap` and `editorBeatmap` are.
For now this is changed to use `playableBeatmap`. A better follow-up
would be to use `editorBeatmap`, but it would probably be best to move
the beat snap bindable into `EditorBeatmap` first.
This matches osu-stable. When the track is running, seeking backwards
(against the flow) is harder than seeking forwards. Adding a mutliplier
makes it feel much better.
Note that this is additive not multiplicative because for larger seeks
the (where `amount` > 1) we don't want to jump an insanely huge amount -
just offset the seek slightly to account for playing audio.