TST: test for plot functions

[aburrell]

This pull request:

1. Breaks up the reusable portions of the default plotting script into functions
2. Adds tests for the plotting script and component functions

TODO:

• Test that plotting script works as expected
• Write unit tests for new functions
• Write unit test for plotting script

[aburrell]

@aaronjridley can you run the plotting script for me and see if it makes sense for you?

1. Switch to this pull request in your repository
2. If you haven't installed aetherpy using python setup.py develop, run that command from the main directory or install in your testing environment
3. Move to the aetherpy\aetherpy directory
4. Run python run_plot_model_results.py and make sure the help commands make sense
5. Run python run_plot_model_results.py with your desired commands to get the plots or movies you want.
6. Tell me about the success or failures of these steps