Keep JSON-LD compacted for ical:status

Most ActivityPub implementations at the moment don't understand JSON-LD (expand and parse it). When they receive an ActivityPub object with the default ActivityStreams context they just handle certain keys available.

Mobilizon also formats all keys fully compacted, despite the ical:status key inside the event object.

I suggest renaming the key from ical:status to status and adding "status": "ical:status" in the context.

This will make adding full-event compatibility with Mobilizon much easier.

Of course, Mobilizon would then need a fallback for federation with older versions, as to my knowledge it does not expand and parse the JSON-LD at the moment.