Unit Testing

[anton-seaice]

In #6, we add an end-to-end/integration test for generating a cice grid from mom. This doesn't completely cover the CiceGrid class, however at this point there is probably limited value in adding unit tests for the class unless we need to do further development on the class.

We also add a couple of utils which should be unit tested:

• md5sum function is covered by test_cice_grid.py but it would be good practice to unit test this
• safe_version function is used, but we should be unit testing the string it returns (noting we can assume the version function is tested / works upstream).