Add an optional desktop shortcut for Windows

closes #3853
Update INSTALL

copy-dependencies.bat did not make it
removed bit-rotting in training-camp map

- crash because Tooltip: Icon: is used in legacy ways
- unbuildable sniper/demo-truck
- no need for custom demo truck with mine layer icon
Documented Gentoo build dependencies 

closes #3869
Add WorldRenderer parameter to WorldLoaded.
Introduce ScreenMap trait for caching screen-coord queries.
Pull ActorMap back out into a trait.
Make ActorMap addition explicit.
Track actor positions in ActorMap.
Remove SpatialBins.
Replace dynamic Actor.Bounds with the (unchanging) relative rect.
Remove PPos hacks from RadarWidget.
Remove unnecessary int2 -> PPos -> int2 conversions.
Remove PPos and tidy DebugOverlay.
Render minefield targeting using PBOG-style overlay.
Replace CenterLocationInit -> CenterPositionInit.
Add WorldRenderer.Position for screen -> world conversion.
Remove PPos hacks from WorldInteractionController.
Fix radar cursor fake mouse event location.
Remove PPos from TeslaZapRenderable.