fixed impasse problem with main vision-blocking bunker in central ridge

* spruced up left flank to give a bit more flavour and detail

large performance push.
* Massively cut down on decal reliance (-88%) and
* reduced splat overhead (-14%)
* reduction in a few choice FX
* additional entities in left flank to make it more interesting

FPS optimisation pass:

*overall reduction in leaf splats
*overall reduction in non-functioning smoke fx
*overall removal of sparrow/bee fx
*overall removal of blowing leaves fx
*overall removal of non-functioning blowing dust fx
*ground texture addition of leaves to compensate for removal of leaf splats
*tapered map corners to reduce dead space
*shortened map description on loading

*overall gain of ~20 fps during tests: 139 fps low, 170 fps high from 115 fps low, 170 fps high

* territory revision - corner intersections now act as cut-offs across the road system. protect these!
* atmosphere changes
* path finding pass
* additional vision blocking hedges added in a few places