The sender PID of the notification was being set to the target PID,
instead of the sender PID. Use correct PID and remove redundant target
PID argument.
Also fix minor accuracy issues.
We can't use slices.Contains anymore since now we are comparing
pointers, and the check would always return false. Replace with using
the Equals function.
Now database getters do error handling aswell, and in case of any error,
the NEX or GRPC method throws a proper error about it.
There are still some doubts on how to handle errors when a list of data
is processed, so for now skip that element on the list and continue.
Also add some constant errors to do better error handling.
Now that we can return errors to nex-protocols-go and it will handle it,
we can improve how errors are being handled in friends.
There's probably room for improvement from this, since I haven't added
error handling on some database getters due to uncertainties on whether
the error should interrupt an action or not.
