Investigate utilizing counters for Song.TotalPlays and Song.CommunityRank

[JudahGabriel]

Raven now supports counters: high performance integer values that can increase or decrease. Changing these values is an ACID operation that doesn't trigger reindexing.

Since re-indexing the entire songs collection is triggered when a user finishes playing a song, or when a user thumbs-up or -down a song, we stand to gain performance by using counters for these values instead.