Finalize streamlit app

[niekdejonge]

The backend is mostly done. The streamlit app still has to be integrated and made more stable.

The structure we have in mind is:

• Basic metadata field uniformication (Do not ask user for confirmation)
• Metadata cleaning and repair. Do ask user for validation.
• Metadata validation. Automatic checks that should pass, before spectra can be uploaded.

The internal structure stores all modifications in the LibraryHandler object.
For all repairs done the user should be able to accept or decline proposed changes by a click. This still has to be implemented in streamlit, but is already implemented in the backend.
The user should also be allowed to make changes manually. A start was made with implementing this in streamlit.