Changes

Add scripts to configure and run convergence test
 This commit contains new scripts created to configure and run
 convergence test simulations. There are four scripts:

 1. run_scripts/run_cnvg_test_multi_cases.csh. This script is used to
    compile and run convergence simulations with specific configurations
    (see details in scripts for explations). After the simulations,the
    space-time convergence plots will also be generated.

 2.run_scripts/convergence_config.py: this script "called" by the
   first script to generate the namelist file for CLUBB-SCM simulations.
   With this script, the modified configuration will be applied in the
   case run directory, while the files in default clubb will not be
   touched

 3.run_scripts/convergence_function.py: this script contains function
   to modify the initial condition profile for convergence test
   simulations. It is called by run_scripts/convergence_config.py
   when the model is configured to use modified initial conditions

 4.run_scripts/plot_l2_convergence.py: this is a sample script to
   generate the space-time convergence plots

Originally committed by Shixuan

reorgnize the scripts for convergence test simulations
Move the script associated with convergence test simulation
in the folder of run_scripts/convergence_run

Originally committed by Shixuan