Integrate HRMP (#258)

* HRMP message ingestion

* Plumb hrmp_watermark to build_collation

* Plumb hrmp_watermark to ValidationResult

* Plumb hrmp outbound messages

* Implement message-broker part of HRMP

* Kill UPWARD_MESSAGES as well

Otherwise, they will get resent each block

* Add sudo versions for easier testing

* Remove the xcmp module

Not useful for the moment

* Doc for HRMP message handler

* Estimate the weight upper bound for on_finalize

* Remove a redundant type annotation

* fix spelling of a method

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Deabbreviate dmp and hrmp in the message ingestion type

* Don't use binary_search since it's broken by a following rotate

Instead use the linear search. We can afford linear search here since
due to limited scalability of HRMP we can only have at most a couple of
dozens of channels.

* Fix the watermark

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

cumulus/primitives/Cargo.toml

@@ -10,6 +10,7 @@ sp-inherents = { git = "https://github.com/paritytech/substrate", default-featur
 sp-std = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
 sp-runtime = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
 sc-chain-spec = { git = "https://github.com/paritytech/substrate", optional = true, branch = "master" }
+sp-core = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
 
 # Polkadot dependencies
 polkadot-parachain = { git = "https://github.com/paritytech/polkadot", default-features = false, branch = "master" }
@@ -33,4 +34,5 @@ std = [
 	"sp-inherents/std",
 	"polkadot-core-primitives/std",
 	"sp-runtime/std",
+	"sp-core/std",
 ]