Defines a Subscription for a push token of a student nation and topic.
This model is used to keep track of every subscription type that a push
token has subscribed to. It is nation-specific, i.e. there will be one entry
for each nation and subscription type that the user subscribes to.
Defines a Subscription for a push token of a student nation and topic. This model is used to keep track of every subscription type that a push token has subscribed to. It is nation-specific, i.e. there will be one entry for each nation and subscription type that the user subscribes to.