Hygiene: Move notification type detection to method

* Moved most of the content from notify to getEventNotifyTypes
* Added phpunit test verifying per-event config overrides defaults
* Remove special-snowflake welcome handling with proper configuration

Change-Id: Ic1aae11d37f23f2b7b8abe3c1edaa414e29be021
Merge "Hygiene: Move notification type detection to method"