Feature: Replace generic Clients in Users service

[dborovcanin]

Is your feature request related to a problem? Please describe.

This is not related to any practical problem.

Describe the feature you are requesting, as well as the possible use case(s) for it.

Currently, the Client concept is shared between Things and Users. While essentially true, we are missing some of the fields that are strictly related to Users, such as username, password, first name, last name, profile photo... Those fields make no sense in Things, but they are important in the UI, and the overall user definition is limited in favor of a generic approach. Let's change that and add those fields to Users, and separate Users from Things.

Indicate the importance of this feature to you.

Must-have

Anything else?

No.