parse interruptionLevel field to allow time-sensitive notifications

[varungupta85]

iOS introduced a new feature called Focus modes in which notifications don't make a sound and don't wake up the screen unless notifications are marked time-sensitive. Notifications can be marked time-sensitive by providing an interruptionLevel. Added support to provide interruptionLevel while adding a notification request.

Fixes #345

[galkn]

Do you know if there is way to configure the amount of time the time-sensitive notification remains on the lock screen? It seems the native reminders app is able to keep them there indefinitely (unless explicitly dismissed), whereas in other cases it is 1-2 hours.

[joebernard]

Can we get this one reviewed? Having time-sensitive notifications is an important feature.