OpenGL2: Add named cubemaps and per-map env.json parsing.

code/renderergl2/tr_local.h

@@ -59,6 +59,7 @@ typedef unsigned int glIndex_t;
 #define USE_OVERBRIGHT
 
 typedef struct cubemap_s {
+	char name[MAX_QPATH];
 	vec3_t origin;
 	float parallaxRadius;
 	image_t *image;