A few linedef action tweaks

• Some improvements to plane scroller actions:
  • Added actions 516-518, 526-528 and 536-538, which affect both floors and ceilings simultaneously.
  • Plane scroller linedefs without a tag will now affect their front sector.
• Added toggle to linedef action 401 to not change the ceiling texture, which was missing for some reason. (Closes #567 (closed))