PR: merge Feat/issue 215/add tests and remove frontend code

[NoveliaYuki]

Description

Leaving kb-server ready to start working on semantic graphs (also known as knowledge graphs).

Tasks completed

• Removed webapp frontend.
• Removed webapp templates.
• Removed frontend folder.
• Removed unused imports from requirements.txt only required by frontend.

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• Moved backend code to the root of lamb-kb-server-stable directory.
• Moved plugin examples to a folder called examples.

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• Removed old testing files.
• Added unit tests.
• Added full backend tests (from route to database).

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• Removed old unused files.
• Removed implementation plan files of things that are already implemented.