Add notification default templates example

[partydragen]

Adds default notification templates for generic contents can be used for most notifications purposes

Keeping it simply sending notifications

$notification = new Notification(
    'mass_message',
    $title,
    $content,
    ....
)

Default email template always contains link, Perhaps register all notifications to nl2_alerts even if alert preference is off? Then all links can be sent to /user/alerts/?id={ID} then it will direct user + mark as read, or if no link is set in alert it wik simply open the rich content page

Another reason having title, content in notification constructer is for future notification types such as discord, not need to update every single alert line to support a new type

I believe AlertTemplate is not needed thought as it already simply just using the title, content, link etc