Add unit tests to index.html validator

- Add unit test to all check functions
- Add unit test to file handler

Changes in swc_index_validator.py

- Remove some calls to `strip()`

  They aren't necessary any more because we use PyYAML.
- Changes in `check_contry()`

  Use only one conditional
- Change in `check_intructor()`

  Check if the list isn't empty.

TODO:

- Fix the unit test that fail.
Merge pull request #1 from r-gaia-cs/validator

Add unit tests