Cross pbs cluster

This update has two purposes:

1) We want dax to be cluster proof. We added a dax_settings to allow the user to change the cluster command with what they use for their cluster. So far, it's working on 'qsub/pbs' cluster.

Changes on the package: we removed the constants.py files and renamed it dax_settings.py. We moved some default value into this file.

2) Going forward, we want to remove masimatlab path from the dax package. Dax should not be affiliated to the work done at Vanderbilt University. 

Changes on the package: We removed all masimatlab path called in the package.