This is a lot easier to manage than having them in the code.
For now it piggybacks on the map hack feature, later this should use the same scripted approach as GZDoom.
* made it palette aware
* use backend facilities to track precached data.
* fixes bug in animation precaching loops - they only precached the base index over and over again.
* 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.
This was by far the messiest game, there's two reasons for this.
First, the portal links do not need to be in an actual portal sector, so they cannot be used to detect portal sectors.
Second, the game moves portals in place, so all offsets are (0,0,0) so that not even these can be used for detection.
The only working method is the super-complicated original way to look up portals at run time, just being done at map start.
Having static portal links should reduce the render glitches quite significantly because the renderer knows now which sectors belong to a portal and can use this information to ensure proper processing.
Unlike the other games these are so poorly defined that the engine has to rely on the original fudging to pick the proper portal to link to. As a result they are just as limited as they always were.
In addition all the portal search code had to be reinstated.
