Refactoring users plugin in webserver

[pcrespov]

Database

users.id
users.name
users.first_name
users.last_name

So i guess I could move it to

users.id
users.user_name
users.first_name
users.last_name

Models

• Update = PATCH, Replace = PUT.
  In any case, I notice we get confused between update and replace. I guess it means we should perpahs start using Patch.

So the model names should be : $ResourceName$Operation where Operation in [Get, Update, Replace, Delete, Create]. Perhaps instead of Update we should use Patch?

Exception handling

• mappers

Originally posted by @pcrespov in #6904 (comment)