Update configuration file so it exports more of vega variables.

Fix warnings related to conversion to string literals to char*

Re-factor the linear solver and sparse integrator

Make solver interfaces more generic makes it easier to plug external linear solver in to the time stepping method.

Conflicts:
	src/util/interactiveDeformableSimulator/interactiveDeformableSimulator.cpp

Some changes to get things building on OS X again.

... when threads and OpenGL support are off.

It looks for the Xmu library even though it is
not a dependency of freeglut3.

... to see if it builds without BLAS/LAPACK.

... now that they are not duplicated in the `include` directory.

This also adds a configuration option named
`VegaFEM_ENABLE_OpenGL_SUPPORT` to match Ricardo's build.