Refactor|World|Map: Continued work on removing the Segment map element (obsolete)
Refactor|World|Map: Replaced more usage of the obsolete Segment map element
Refactor|World|Map|Line: Link map lines directly to half-edges (bypass Segment)
World: Cleanup
Client|Map Renderer: Cleanup
Refactor|World|Map: Continued whittling away at Segment

What ultimately remains of this component will be found a new home.
World|BSP Builder: Only produce Segments for the half-edges of map line sides

In the case where an edge is produced automatically when partitioning
space into convex subspaces a line segment is unnecessary (these will
never be drawn as (implicitly) they have no surfaces).

The geometry/topology information is all that is needed in this case,
which, is now modeled with half-edges.
World: The parent of a segment is the Line::Side for which it was produced
Server|World: Trimmed unused fat from Segment that is not needed server side

Todo: Strictly speaking the server does not need segments at all any
more, so it would be good to get rid of them completely...
Refactor|World: Simplified Segment (no need for a private => public inst reference)
Refactor|World: Converted Segment into a subcomponent of Line::Side

What remains of the old Segment component now only makes sense in
the context of a Line::Side. Making this a Line::Side subcomponent
presents many opportunities to not only clean up the APIs of these
classes but allow various logics to be pushed up to a higher level
in the map element hierarchy.

Todo: Line::Side should take ownership of the segments and provide
an API for dynamically managing these.
Refactor|Client|BiasSurface: Bias surfaces no longer need to expose their BiasTrackers
World|BspLeaf|ConvexSubspace|Line: Cleanup
World|Line: Line::Side has ownership Segments; basic API for management

In the future this mechanism will be replaced entirely, so for now
this simple implementation will suffice.

Todo for later: Both BspLeaf and Line::Side now implement a similar
mechanism for management of "subelement geometries". This mechanism
should be generalized with a uniform (likely URI based) method of
addressing geometries (libdeng2's Bank seems to be a good fit).
Merge branch 'master' into remove-segment