Add application license

[djperrefort]

Decide on a license type and add the appropriate licensing information to the source code.

This issue will require some internal team policy decisions. Look to internal team documentation for the most recent updates.

Changes that need making:

• Add a license file
• Add the __license__ variable to __init__.py
• Update the setup.py file
  • Add the license argument to the setup function call
  • Update the classifiers argument with the correct license type
• Update (dynamically) values in the docs/source/conf.py file