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