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Notification - base class
By convention a Notification has a type and a value. Derived classes can add
extra properties or methods.
NotificationType: Notification Type
Ident: Can be an ident, or for simple messages a value that needs transmitting.
IsDistinct: non zero if this message supercedes previous messages of this type.
Distinct messages are usually sent often and self contained
(i.e. no relative state changes such as toggle value)
Messages that indicate an event (such as after a pilot action)
will usually be non-distinct. So an example would be gear/up down
or ATC acknowledgements that all need to be transmitted
The IsDistinct is important for any messages that are bridged over MP as
only the most recently sent distinct message will be transmitted over MP.
Example:
position update, where only current position is relevant -> IsDistinct=1;
0 = queue all messages for MP bridging
1 = queue only latest message (replace any old message of same type+ident)