* removed the long defunct EDuke32-based map art system. With our move to named textures this will not work anymore so fixing the existing problems would be pointless.
* moving .def related parsing stuff out of buildtiles.cpp.
* some initial refactoring to make the tile store a static, non-modifyable resource after initial setup.
No GC yet, only the classes have been altered and some GC-related features been added.
Full switchover will require adding GC support to all data in the game.
* moving polymost_voxdraw into polymost.cpp.
* consolidated all remaining voxel code in hw_voxels.cpp. All original Build voxel code is completely gone now, except for polymost_voxdraw, so this got moved out of the build/ folder.
* integrate Blood's voxel init code into the main function.
* some further cleanup was allowed as a result of this, so engineInit is gone now because these parts can now be done outside the games' app_init functions.
