No traction condition for contact algorithm

[WaveHello]

Traction condition from Base algorithm follows Bardenhagen et al. (2001) is not implemented for the contact algorithm. The traction is calculated but there isn't an if statement to actually be able to use it to track if contact should be applied. Is in subroutine ApplyMPMDynamicContact().

[WaveHello]

Added the required update:

if (traction < 0.0 or. DiffDotUn>0.0 .and. traction == 0.0) then 

right before the following comments

!If the modified contact model is used, correction is done when Traction < 0 (compression)
! The exeption is when it is the first contact and all stresses are still zero: 
!    - this will give Traction = 0

[WaveHello]

Changed update to (on Anura3D_VelCorrection branch)

if (traction < 0.0 .and. DiffDotUn>0.0 or. DiffDotUn>0.0 .and. traction == 0.0) then 

even if the traction condition is used the difference in velocity should still be checked.