Fix the Firebase security rules

[wescopeland]

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[wescopeland]

At a very high level:

avatars: Only editable by that specific user and if they have profileScore >= 20.

badges: read-only for the time being

contests: need an organizer property. activeGames and properties are only writable by the organizer. playerPool is writable by registered users while the event state is "upcoming". when the event state is not "upcoming", it is only writable by the organizer. recentActivity writes should be a server-side operation triggered by a client function.

standings: this will be a server-side write triggered by a client function.

users: profileScore property needs to be removed as it has been migrated to badges. should be writable only by the user and readable by all.