add hardware_id column to default_users table

[richjoslin]

I (and assumedly others) would like a field to store an arbitrary hardware ID which can be passed in from a client device (laptop MAC address, iPhone UDID, etc) and can be used for security purposes. This is more intended to be used with client apps (such as mobile apps) which are using Rivety for REST API endpoints.

Along with the new db field, a new MCA for passing in a hardware ID, and it just updates the current user's hardware ID and does nothing else. The endpoint would only be accessible to users that are logged-in.

[richjoslin]

I've got this done in a fork and just need to merge it back.