Refactored existing user API work

- Updated routes to use new format.
- Changed how hidden fields are exposed to be more flexible to different
  use-cases.
- Updated properties available on read/list results.
- Started adding testing coverage.
- Removed old unused UserRepo 'getAllUsers' function.

Related to #2701, Progression of #2734

app/Auth/User.php

@@ -72,7 +72,7 @@ class User extends Model implements AuthenticatableContract, CanResetPasswordCon
      */
     protected $hidden = [
         'password', 'remember_token', 'system_name', 'email_confirmed', 'external_auth_id', 'email',
-        'created_at', 'updated_at', 'image_id',
+        'created_at', 'updated_at', 'image_id', 'roles', 'avatar',
     ];
 
     /**