Add container interface to get notifications
Add notification classes
Add notification config and ext requirements
Add notification language files
Call notifications when adding or removing from groups
Simplify logic of default setting condition
Adjust lang var name for notifications
Update ext.php removing code duplication
Minor param doc block fix
Add missing doc block parameter
unset referenced value in foreach loop
Merge pull request #15 from VSEphpbb/fixes

Minor fixes
Merge pull request #14 from VSEphpbb/add-notifications

Add notifications support