[ticket/15883] Review changes
PHPBB3-15883

[ticket/15883] Add error for invalid usernames being added to a group
Update the ACP and the UCP so that when bulk adding users to a group,
if invalid usernames are submitted alongside valid usernames then a
message will be displayed to inform the user what the invalid usernames
are.

PHPBB3-15883

[ticket/15883] Use the new language object
Using the new ->lang() format. Made the username
comparison case insensitive. Also fixed a bug where the return to
previous page link in the UCP was going back to the list of
groups rather than the specific manage group page when an error
occurred.

PHPBB3-15883

[ticket/15883] Doc block change
PHPBB3-15883

[ticket/15883] Doc block change
PHPBB3-15883

[ticket/15883] Review changes
PHPBB3-15883

[ticket/15883] Use the new language object
Using the new ->lang() format. Made the username
comparison case insensitive. Also fixed a bug where the return to
previous page link in the UCP was going back to the list of
groups rather than the specific manage group page when an error
occurred.

PHPBB3-15883

[ticket/15883] Add error for invalid usernames being added to a group
Update the ACP and the UCP so that when bulk adding users to a group,
if invalid usernames are submitted alongside valid usernames then a
message will be displayed to inform the user what the invalid usernames
are.

PHPBB3-15883