Frontend: Documentation - Project Structure

**Describe the solution you'd like**
The file structure and important files of the frontend-template should be documented and described.
A table-based documentation which short information about the purpose of folders and files must be created.

**Describe alternatives you've considered**
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**Additional context**
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Start by inspecting the frontend-template and inventorying its folders and important files. Create table-based documentation with short descriptions of each folder and file, and consider the work done when the frontend structure and file purposes are documented.

Written by the indexing model from the issue text.