Ignore playhead when finding delta from edit position for main clocks

Ignore playhead when finding delta from edit position for main clocks

Pass 'ignore_playhead == true' to Editor::get_preferred_edit_position()
when calculating offset of the primary and secondary main clocks if 'delta
to edit cursor' is selected, so that if the edit point is playhead, the
selected marker (if any) or mouse position will be used as the delta origin
instead.