models Stat and User have inconsistent data types for Date

[pieteradejong]

in stat.coffee:
date: String

in user.coffee:
createdAt:
type: Date
default: Date.now

Actually, it seems from the docs (see link below) that createdAt is part of the ObjectId, so to avoid redundancy we could just store updatedAt. Would it be correct to assume we need updatedAt in order to display that in the UI?

link:
http://docs.mongodb.org/manual/reference/object-id/#ObjectIDs-TheBSONObjectIdDatatype