Removing Blender Game Engine from Blender 2.8

Folders removed entirely:
* //extern/recastnavigation
* //intern/decklink
* //intern/moto
* //source/blender/editors/space_logic
* //source/blenderplayer
* //source/gameengine

This includes DNA data and any reference to the BGE code in Blender itself.
We are bumping the subversion.

Pending tasks:
* Tile/clamp code in image editor draw code.
* Viewport drawing code (so much of this will go away because of BI removal
  that we can wait until then to remove this.

CMakeLists.txt

@@ -598,6 +598,7 @@ if(NOT WITH_SDL AND WITH_GHOST_SDL)
 	message(FATAL_ERROR "WITH_GHOST_SDL requires WITH_SDL")
 endif()
 
+# python module, needs some different options
 if(WITH_PYTHON_MODULE AND WITH_PYTHON_INSTALL)
 	message(FATAL_ERROR "WITH_PYTHON_MODULE requires WITH_PYTHON_INSTALL to be OFF")
 endif()