Fixed #23744 -- Fixed typo in selenium testing example.

Thanks djbug for the report.
Fixed #5405 -- Added support for reStructured text in admindocs for model docstrings
Made changes asked in review by MarkusH

- Renamed TestDocstrings to more apt name TestUtils
- Wrote tests for methods in utils
- Made small changes in docstrings in utils to comply to PEP 257