This replaces *_NewMap with *_NewScene and adds SCR_NewScene to handle
loading a new map (for quake) in the renderer, and will eventually be
how any new scene is loaded.
Still work with gcc, of course, and I still need to fix them properly,
but now they're actually slightly easier to find as they all have vec_t
and FIXME on the same line.
GL still has its own functions for enabling and disabling fog while
rendering, but GLSL doesn't need such (thanks to the shaders), nor will
vulkan (and the software renderers don't support fog).
While there's currently only the one still, this will allow the entities
to be multiply queued for multi-pass rendering (eg, shadows). As the
avoidance of putting an entity in the same queue more than once relies
on the entity id, all entities now come from the scene (which is stored
in cl_world in the client code for nq and qw), thus the extensive
changes in the clients.
