Show the cursor of the followed player in surveillance

A label under the camera shows what the player being followed holds in
their cursor, item and count or the ghost item, so that using a
deconstruction planner or similar can be seen. It is hidden while the
camera shows a fixed location.

Closes #427

exp_scenario/module/locale/en.cfg

@@ -489,6 +489,9 @@ caption-set-location=Set
 type-player=Player
 type-static=Static
 type-loop=Loop
+caption-cursor=Cursor: __1__ x__2__
+caption-cursor-ghost=Cursor: __1__ (ghost)
+caption-cursor-empty=Cursor: empty
 
 [exp-gui_task-list]
 caption-main=Task List [img=info]