Added: Grabbable, Hand

Generalized grabbing mechanism for use with runtime world editing.
Refactor: Extracted HueCircle, HueCircleVisual from edit_bias.cpp

C++ implementation of the hue circle manipulator.
Refactor: Extracted BiasSource from rend_bias.cpp

C++ implementation of a Shadow Bias (light) source.
Refactor: Extracted BiasSurface from rend_bias.cpp

C++ implementation of a Shadow Bias surface.
Refactor: Revised VertexIllum and BiasTracker

Also removed obsolete Shadow Bias components.

Todo for later: Replace BiasTacker with de::BitField.
World: Integrated Hand and added FrameBegin, FrameEnd audiences

Plus some minor rename refactorings.
Shadow Bias: Integrated BiasSurface, optimized linking mechanism

The previous implementation maintained a global linked list of all
the bias surfaces in the map. This meant that the unlink algorithm
(which had to support dynamic unlinking) was of the order O(n) and
consequently unlinking often took far longer than it should.

The revised mechanism dispenses with the global list entirely and
instead a simple traversal of the Map element LUTs is used when
performing bias lighting updates.
Refactor|Shadow Bias: Relocated and map-space shadow bias editor visuals

The in-map visualizers for various components of the shadow bias
editor (including the cursor and source labels) were updated to
use libdeng2 features and moved to rend_main.cpp

Also updated the GUI widgets.
Cleanup
Merge branch 'master' into shadow-bias-c++
Cleanup: Define MAX_BIAS_SOURCES in de::Map
Refactor|Shadow Bias: VertexIllum now internal to BiasSurface

Only BiasSurface needs knowledge of/access to this data.
Refactor: Renamed rend_bias.cpp/h as biastracker.cpp/h respectively
libdeng2|Added: Overload of de::fequal() with precision argument
Refactor|BiasSurface: Continued reworking and cleaning up BiasSurface
BiasSurface: Cleanup
BiasSurface: Cleanup
Merge branch 'master' into shadow-bias-c++

Conflicts:
	doomsday/client/src/world/world.cpp
Merge branch 'shadow-bias-c++' of github.com:skyjake/Doomsday-Engine into shadow-bias-c++
Merge branch 'master' into shadow-bias-c++