Display selected vertices in demo app

[lucasimi]

Since Streamlit v1.35, it's possible to capture user selections from Plotly charts. Incorporating this feature into the demo app would be beneficial, as it would allow to display aggregated statistics on subsets of the Mapper graph. This enhancement would provide users with more interactive and insightful data analysis capabilities.

[lucasimi]

Unfortunately, it's not possible to use Streamlit v1.35 since it would bring a regression due to this issue.