Added WorldChunkMap for world streaming in TilePathScene.

TilePathScene can now be scrolled all around the World.

WorldChunkMap is based on LotPackViewer's chunk map code (which was based
on lemmy's).
TilePainter can paint whole maps.

This is the new equivalent of putting a Lot into a map.  The TilePainter
simply paints the map's tiles into the world, replacing whatever tiles are
already in the world but not removing any tiles where none exist in the
source map.
Fixed a tolua bug.
Defined lua_assert() to an external function that calls qt_assert().
Fixed off-by-one error when adding objects to WorldQuadTree.

QRect right==left+width-1  and bottom=top+height-1, unlike QRectF where
right==left+width and bottom=top+height;
Support multiple tile layers in WorldChunkMap etc.
Fixed an off-by-one bug with TilePainter::fill().
Attempted to fix drawing paths in isometric views.

When painting the exposed part of PathLayerItem, convert the rectangle in
item coordinates to a world-coordinates polygon to test which paths are
on screen. *** Something is broken somewhere.
Removed use of Map/MapComposite/ZLevelRenderer from TilePathScene.

Now TilePathRenderer does the work of ZLevelRenderer without needing to
hack use of Map/CompositeLayerGroup.
Added PathWorld.

PathWorld is the new path-based world, rather than overloading the existing
World class.
Renamed various PathWorld::layer* to PathWorld::pathLayer*

This is to distinguish between path layers and tile layers.
Removed the WorldPath namespace.

WorldPath::Path -> WorldPath
WorldPath::Node -> WorldNode
WorldPath::Layer -> WorldPathLayer

Removed typedef'd Point/Rect/Polygon/coord_t as well.
Use PathWorld::tileWidth()/tileHeight()/maxLevel() instead of constants.
Fixed format issue in buildingmap.h.
WorldLookup uses separate QuadTrees for nodes/paths/scripts, preserves order.

WorldLookup was returning paths/scripts in arbitrary order, now they are
returned in the order they appear in the world's lists of paths/scripts.
Begin implementing path tools.

WorldLookup keeps separate node/path quadtrees for each path layer.