Egress queue validation in runtime (#155)

* Add fn to validate egress routes

* Add blank tests

* Reject routing to non existent parachains

* Reject if routing to self

* Reject if egress route parachain ids out of order

* Extract method for checking egress routes

* Reject empty egress routes

* Extract test method

* Generate empty trie root constant in build script

* Remove unwraps

* Hardcode EMPTY_TRIE_ROOT and add test to verify

* Const not pu

polkadot/runtime/src/lib.rs

@@ -70,6 +70,9 @@ extern crate polkadot_primitives as primitives;
 #[cfg(test)]
 extern crate substrate_keyring as keyring;
 
+#[cfg(test)]
+extern crate substrate_trie;
+
 mod parachains;
 mod claims;