Removed viscous normal force in the friction law.
- visualizing Brownian stress
- cleaning
Minor bug in StressTensor class .
.
New feature for initial relaxation
When the chosen parameter file is “init_relax.txt”, the final configuration is saved in the directory named “after_relax”.
Fixed a bug of Brownian stress due to the timing of constructing the full velocity from predictor and corrector velocities.
Adding averaging functions for stress
Merge remote-tracking branch 'refs/remotes/origin/master'

Conflicts:
	LF_DEM/System.cpp
Fixed stress averaging algorithm.
Added missing resettings in the stress averaging codes (minor bug).
Fixed a memory leak.
Cleaning.
Cleaning.