Fixed: Map renderer draw state refactoring oversight
Refactor|BspLeaf: Separated Face geometry from BspLeaf
BSP Builder: Implementation improvements

LineSegment has been revised to follow the design "pattern" of the
Line class component. All line segments in the plane now have two
actual sides, irrespective of whether there are sectors on one or
both sides the map line.

Splitting line segments and building new ones along partition lines
was revised to factor out the ugly duplicate-then-update logic of
the previous implementation.

Todo: HPlane presently duplicates a little of the functionality of
LineSegment. A new abstraction is needed here.