Notification distribution

[0xf104a]

The general idea of issue is to make notifications available for other apps by broadcasting them as intents. This would enable other developers to use this app as notification distributor. The genaral implementation plan as follows:

• Create own permission for other app receiving intent
• Create an intent distributor which would pack notification(both its parsed part and raw version)
• Create an API which would allow apps with abovementioned permissions to disable some notification channels, so we avoid duplicating notifications

See #10 (comment) and stefan-niedermann/nextcloud-deck#1638 (comment)