Fixed #5405 -- Added support for reStructured text in admindocs for model docstrings

Refered to PR #760 for help
@elvard wrote code to support it, but it needed to be modified, in order to merge
@gkmngrgn added tests that also needed to be modified
Squashed commits:
[39a9318] Made changes asked in review by MarkusH

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