Update plotly theme used for 3D figures #102

Right now for the 3D figures the used plotly theme is not defined manually. This means that when running inside streamlit, the 'streamlit' theme is used, but in other cases (like Jupyter Notebook) it's 'plotly'. Might be worthwhile to unify this, or make it an option.

I like 'streamlit' more than 'plotly', but it's only available when streamlit is installed, so not in all cases. That means, either use another theme as default, or hardcode/import the streamlit version.