Adding "date earned" for achievements

[sedgwick]

Currently there's no way to see when a player earned an achievement, and when a player has many achievements it can be hard to keep track of new ones. So sometimes I'll notice i earned an achievement while I was away, but have no way of knowing which it was when I have over 130 achievements.

[seiyria]

One way to do this is to keep a hash of when a user originally achieved something, ie,

{
   "Impossible I": new Date()
}

This way we can still overwrite achievements as necessary (for modifications, etc), and not worry about that data changing as often as it does.