mhd init

New file

• transformation_3d.py : new routine for transformation between logical domains
• test_mhd_init.py

Modified file

• mhd_init.py : Read the parameters.yml file and initialize the all the mhd variables
• domain_3d.py : new function 'transformation' for transformation between logical domains
• parameters.yml : new input values for initialize mhd variables
• cc_lin_mhd_6d.py : main code also modified suitable for new mhd_init
• test_domain.py