Add Delivery Groups to Pushover

[zandercodes]

💡 The Idea
Is there a way to add groups to Pushover delivery?
https://pushover.net/api/groups

🔨 Breaking Feature
Currently you can only send to devices, but you have the possibility to create delivery groups in Pushover, where you write to all devices and send them to the delivery group.
Because there is also the case that devices are not in their own account of Pushover and then you can only send them to several via a delivery group.