Firebase secure deployment support

[nathanjones4323]

This package is awesome! My only problem was that I need to persist the data with firebase, but I can't push my firestore-key.json file to GitHub for security.

This PR uses the method from this blog post to read the firebase credentials from st.secrets in addition to directly from firestore-key.json

• Adds support for using firebase to persist analytics securely when deployed through Streamlit Cloud or self hosting
• Adds support for nested dicts with non-string keys
• Added to documentation on usage inside README.md
• Tested locally with my firebase credentials
• Display widget usage stats in pandas.DataFrame instead of a single dict

[nathanjones4323]

Link to Streamlit discussion on this PR

[nathanjones4323]

Resolves Issue #29

[nathanjones4323]

@jrieke Let me know if you need me to update anything or have questions !

[jgieseler]

Would be really nice if this PR would be merged at some point...

[abrayne]

I would also like a solution of this kind

[444B]

FYI this PR was integrated into version 0.7.0 of streamlit-analytics2 downstream fork (latest version 0.7.7 at time of writing)