Dissolve database schemas

[jh-RLI]

Summary of the discussion

For a long time we used sql database schemas to group out data into multiple categories. This was a suboptimal decision which we will now rework.

As schemas are widely implemented in the current code this is a substencial rework of our codebase mainly the API & DATAEDIT apps are affected.

Other apps also use table data but we should be able to manage to keep the interfaces consistent or implement a new version of interfaces. (The best solution for this must be determined first)

Type of change (CHANGELOG.md)

Added

• Add a new functionality (#)

Updated

• Reworked api/views.py code to be more modular by introducing decorators.py and utilities.py modules (#)
• Tables are now stored in both: the old databse schemas and the new database schemas

Removed

• Remove a broken link (#)

Workflow checklist

Automation

Closes #1356

PR-Assignee

• [ ] 🐙 Follow the workflow in CONTRIBUTING.md
• [ ] 📝 Update the CHANGELOG.md
• [ ] 📙 Update the documentation on mkdocs

Reviewer

• [ ] 🐙 Follow the Reviewer Guidelines
• [ ] 🐙 Provided feedback and show sufficient appreciation for the work done