Change snoozing behavior for notifications in groups

- Snoozing a summary notification will snooze its current
children in addition to itself
- Posting a non-snoozed notification to a summary will
unsnooze the summary
- snoozing the only child of a group will also snooze the group
summary

Test: runtest systemui-notification
Change-Id: I5edba1461a59131c6c202f02e6f89404d22bb404
Fixes: 35934956