Add a firebase model for sessions

[joshprzybyszewski]

What data do we need in the firebase model?

• String game style ("Normal" or null, "Four Corners", "T", etc)
• List<String> what words are used for the session
• UserID curator
• DateTime start time
• DateTime end time
• Geographical Point geolocation
• Map<UserID, List<DateTime>> time of bingo for a player
  • TODO? validate the bingo of that player
  • TODO: pub/sub in firebase: broadcast out bingoes (phase 2)
• List<UserID> who is in the session
• Document what wordbanks document it's based off

For firebase supported data types: https://firebase.google.com/docs/firestore/manage-data/data-types

[cszczepaniak]

Is it safer to use an enum for game style?

[joshprzybyszewski]

It would be safer to use an enum, but per-the-link firebase doesn't define enums, so I think a string is the most clear alternative.