function to trigger nullification period, tests for the new functionality and expansion of NetworkData trait

Signed-off-by: Uncle Stretch <uncle.stretch@ghostchain.io>

pallets/traits/src/networks.rs

@@ -38,4 +38,5 @@ pub trait NetworkDataMutateHandler<Network, Balance>: NetworkDataInspectHandler<
     ) -> Result<(Balance, Balance), ()>;
     fn accumulate_commission(commission: &Balance) -> Result<Balance, ()>;
     fn nullify_commission();
+    fn trigger_nullification();
 }