OpenVSP 2.9.0, first public alpha for version 3.

For the past two years, a dedicated team has been re-writing VSP from
the ground up.  This is the first public release from that effort.

The core v3 team responsible for this work so far is:
Alex Gary, J.R. Gloudemans, Yue Han, David Marshall, and Rob McDonald

The 2.9 series will be the alpha and beta versions leading to 3.0.0, which
will be the first production release for this branch.

Unfortunately, this development was done in a way that the development
history is not a meaningful continuation of the 2.X history.  Consequently,
this commit starts a new history from the beginning.  Do not try to work
across the branches, no good can result.
Change library search order to prefer built-in libraries over system libs.
Clear up abs/fabs ambiguity to make older compilers happy.
Fix nasty FLTK interaction with Update
Change Update() calls to delayed updates.
Fix formatting of main screen version number handling.
Comment out Vehicle UpdateBBox to prevent infinite loop.
Fix CMake on Linux case sensitivity problem
Update Code-Eli to latest master.

Includes fix for X11 collision with Eigen on Linux.
Change library linking order to get VSP to build on Linux
Add pthreads on Linux
Add -fPIC flag for x86_64 on Linux.

The Position Independent Code flag is needed for shared libraries on some
platforms.  This is normally implied for shared libraries, but we build
most of VSP as static libraries, so it is not set automatically.

Later, we use these static libraries to build a shared library for the
Python bindings.  So, for dual-use libraries, we need to set -fPIC manually.
Re-order libraries for Python bindings.
Added SceneObject class.  This class is the base class for all "Scene" objects.
Removed geometry type parameter from all scene objects' constructor.  All geom type are set through the setGeomType() function now.
Function name changes.
Added singleton pattern to ColorCoder.
Modified Renderable to derive from SceneObject.  Removed duplicated functions.  Changed some function names.
Added Pickable and Selectable.  Pickable allows an object or its vertices to become pickable.  Selectable stores picked results.
Updated all Renderable objects(Entity, Marker) with SceneObject changes.