Adding a warning for Brownian stress computation
Merge remote-tracking branch 'origin/master'
merge remote.
merge remote
Merge remote-tracking branch 'origin/master'

Conflicts:
	LF_DEM/Interaction.h
	LF_DEM/Simulation.cpp
	LF_DEM/System.cpp
	LF_DEM/System.h
merge remote
Merge remote-tracking branch 'origin/master'

Conflicts:
	LF_DEM/System.cpp
	LF_DEM/System.h
Ongoing work on Trilinos.

Primary implementations:
- basic allocations : vectors, matrix, solver
- fillSparseResMatrix() method
Early TRILINOS implementation

Trilinos is now "implemented" for non Brownian part.
Right now it compiles, but fails at runtime.

You can switch back to working version based on Cholmod by setting a
 preprocessor definition in System.h.
Merge remote-tracking branch 'origin/master'

Conflicts:
	LF_DEM/Interaction.h
	LF_DEM/System.cpp