DisplayName change field

During user creation in "element-admin" it would be desirable to predefine their displaying name which is mandatory in working environment. Otherwise, in order to set display name there's no other way than using `mas-cli`, which is very inconvenient and makes it impossible to delegate task to others.

As a solution, it would be great to have an additional field on user creation for setting display name. For an already existed user, displaying name could be an interactive field in a way it is made in element web client.

Examples are on pictures.