#4 mod-customizable code in external files

[Eugene Bujak]

the idea - the mod-independent code (handling XML,
parsing entities and such) and mod-dependent code
(like in spectator mode using teleporters, passing
through doors and other things) should be separated.

this should be done by adding a new set of functions
and files. The functions and files should be organized
the way, that they will not impact the overall
playback ability, and they must survive opendemo
version updates.