XCM revamp & Ping pallet (#391)

* Add spambot

* Fixes

* Add some extra functions to spambot, bump version

* Lock..

* Aggregate HRMP (XCMP/HMP) messages. Payloads for spambot.

* Fix tests, bump Polkadot.

* Fix HMP tests

* Rename Hrmp -> Xcmp for handler/sender

* Use master branch

* Test Xcm message passing & rename away from HMP

* Docs

* Introduce fee payment mechanics into XCM.

* Rename spambot -> ping

* Lock

* XCMP message dispatch system reimagining

- Moved most of the logic into xcm-handler pallet
- Altered the outgoing XCMP API from push to pull
- Changed underlying outgoing queue data structures to avoid multi-page read/writes
- Introduced queuing for incoming messages
- Introduced signal messages as a flow-control sub-stream
- Introduced flow-control with basic threshold back-pressure
- Introduced overall weight limitation on messages executed
- Additonal alterations to XCM APIs for the new system

* Should process any remaining XCM messages when we're not doing anything else.

* Update API usage and preparation for the big build.

* Some build fixes

* Build fixes

* xcm-handler builds

* Fix warnings

* Docs

* Parachains system builds

* Parachain runtime building

* Fix build

* Introduce transfer_asset specialisation.

* Fixes

* Two-stage upgrade for parachains.

* Fixes

* Fixes

* Updates for message sending.

* Repotting/renaming. Add primitives/utility.

* Remove real-overseer and bump refs

* Configure & document Rococo XCM runtime.

* Add shell runtime, some companion changes for #8589

* Bumps & fixes

* Fix test

* Build fix

* Update pallets/xcmp-queue/src/lib.rs

Co-authored-by: Amar Singh <[email protected]>

* Make tests compile

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <[email protected]>

* remove unused

* remove unused event stuff

* Adds proper validation-worker to make integration tests work

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <[email protected]>

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <[email protected]>

* import saturating

* remove panic test

Co-authored-by: Robert Habermeier <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>
Co-authored-by: Amar Singh <[email protected]>
Co-authored-by: Shawn Tabrizi <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>