Refactor all UI docstrings

This will make the UI docs look much better
Merge pull request #1341 from elyezer/docstring-refactor-ui

Refactor all UI docstrings
Trim down test_multiple_paths.py

Make all all tested entities (i.e. classes in entities.py) inherit from
`EntityReadMixin`. Take advantage of this fact to trim down module
`test_multiple_paths`.

Add a logger to module `test_multiple_paths`. Log out information in several
tests, thus allowing the assertions to be trimmed down.