username without control for admin and users

Admin user and simple user can modify username without control

• if admin change his/her username with one that already exist, he/she cut yourself out
• for simple user is the same

On both cases, user form saving done without "userExists" Ajax post control

• Admin need to be allowed to change username, but with "userExists" Ajax post control, like as user creation

• Simple user shouldn't be allowed to username modify, because entity "Updates" integrity in "Entity Summary" view