core: move a few misorganised hotkey declarations

move the clear playlist and subtitle scaling hotkey options above
the bookmarks and jump-size ones.

 - in the hotkey widget they are surely more interesting than the
   big block of bookmark ones that otherwise come at the end.

 - in help output, since the bookmark ones and jump sizes ones each
   declare sections, these options appear miscategorised as being a
   part of the bookmark section. this was overlooked in
   711733c6, or more likely perhaps
   lost from it in a rebase over time.

(cherry-picked from 1cbb4d39).