Merge exits and exit tops into single object

[Nami Verasche]

http://www.lemmingsforums.net/index.php?topic=2718.0

Possible reason against this is the use of exit tops for decoration in some cases.

[Nami Verasche]

Experimental code (VExNf1.45n) can handle the conversion of existing levels to such a system.

[Nami Verasche]

At this point experimental code handles it, and all converted graphic sets are generally being updated to do so. Exceptions exist where eg. the exit is a lockable one, and thus needs seperate parts (one always animating, the other showing the unlock animation).

[Nami Verasche]

This has been done for all standard graphic sets where practical to do so.