Install page - Handle invalid administrator username better (#7060) (#7063)

* Install page - detect invalid admin username before installing

* Also fix #6954

options/locale/locale_en-US.ini

@@ -93,6 +93,10 @@ sqlite_helper = File path for the SQLite3 database.<br>Enter an absolute path if
 err_empty_db_path = The SQLite3 database path cannot be empty.
 no_admin_and_disable_registration = You cannot disable user self-registration without creating an administrator account.
 err_empty_admin_password = The administrator password cannot be empty.
+err_empty_admin_email = The administrator email cannot be empty.
+err_admin_name_is_reserved = Administrator Username is invalid, username is reserved
+err_admin_name_pattern_not_allowed = Administrator Username is invalid, username is pattern is not allowed
+err_admin_name_is_invalid = Administrator Username is invalid
 
 general_title = General Settings
 app_name = Site Title