[frontend] Use session gravatar hash in header
mongoose.Schema.Types are different from mongoose.Types, so keep the same names in mongo.js too
[frontend] GET and PUT /users, plus new REST scaffolding with error and etags handling
[apitest] Drop old tests and start with new for /users, and fix error unearthed by them
Update README to new API
Handle MongoError on duplicate key
Include _perms in /users API response objects
[core] Fix incorrect _.extend() usage
Merge pull request #34 from commonsmachinery/user-endpoint

User endpoint