Implement non blocking mutate functions

[wtrocki]

Definition of the problem

Offline requests block promises.
This will mean that code in then will never be called until the device becomes online.

return this.apollo.mutate<Task>().then((retry)=>{
	// Never called when offline.
	// This will be resolved only when online
}).catch((error)=>{
	// Never called when offline
	// This will be resolved only when online
});

Proposal 1

Return error when change is enqueued offline and resubmit every change using client.

return this.apollo.mutate<Task>().then((retry)=>{
   // Never called when offline.
   // This will be resolved only when online
}).catch((error)=>{
  if(error.conflict){
    // User will get error with conflict
  }
});

Proposal 2

Return another observable or promise in error

return this.apollo.mutate<Task>().then((retry)=>{
   // Never called when offline.
   // This will be resolved only when online
}).catch((error)=>{
  if(error.offlinePromise){
    offlinePromise.then((data)=>{
       // Will be called when we become back online
    });
  }
});

[wtrocki]

done in #10