CIDC-1067 some perfecting tweaks

[scvannost]

What

Lots of small tweaks to perfect current implementation of relational db

Why

Extends CIDC-1067 to fix small bugs and differences with the original schemas.
Extra worksheet of Essential Participant Data on tissue slides.
Found a few bugs while writing some developer documentation.

Checklist

Please include and complete the following checklist. You can mark an item as complete with the - [x] prefix:

• Tests - Added unit tests for new code, regression tests for bugs and updated the integration tests if required
• Formatting & Linting - black and flake8 have been used to ensure styling guidelines are met
• Type Annotations - All new code has been type annotated in the function signatures using type hints
• Docstrings - Docstrings have been provided for functions
• Documentation - README has been updated to explain major changes & new features
• Package version - Manually bumped the API package version in setup.py