Originally AUTH_USER_CHANGE handler could modify the user data, however,
auth plugin consequently worked with different copy of the array thus
effectively preventing any changes by the AUTH_USER_CHANGE implementer.

Microfix

many PHPDocs
some unused variables
some dynamically declared variables declared

remove config option

This request makes "Your last update" of the extension info shown when
clicking more info triangle mark. The first installed date of the
extension may not be necessary for local site admin work.