Node-side subsystems for Disputes (#2566)

* dispute subsystem files

* rename

* fix linkcheck

* flesh out section README

* coordinator schema

* DisputeCoordinatorMessage

* stub & coordinator protocol

* dispute coordinator

* add some more message fields

* move links to bottom

* dispute participation

* Cleen It Up !

* runtime: store candidate receipts in dispute state

yeah, this is a little heavier. why are you reading this?

* Revert "runtime: store candidate receipts in dispute state"

This reverts commit 51c10bfd4d866e287e6bd88f317ed57ed987eaee.

* add dispute availability statement type and prepare for availability

* add 'spam slots' to disputes runtmie

* return Spam Slots info from runtime

* rework `ImportStatement` to `ImportStatements`

* some more methods for dispute coordinator

* candidates-included runtime API

* algo for providing disputes to runtime.

* handle signing with coordinator

* dispute coordinator chain ops

* remove dead file

* remove keystore from dispute participation

* adjust ApprovedAncestor to return the necssary data

* discuss how approved ancestor and determine undisputed chain are used together

* add TODO

* initiate disputes from approval voting

* route statements from candidate backing and approval voting

* fix guide build

polkadot/roadmap/implementers-guide/src/runtime-api/candidates-included.md

@@ -0,0 +1,8 @@
+# Candidates Included
+
+This runtime API is for checking which candidates have been included within the chain, locally.
+
+```rust
+/// Input and output have the same length.
+fn candidates_included(Vec<(SessionIndex, CandidateHash)>) -> Vec<bool>;
+```

polkadot/roadmap/implementers-guide/src/runtime-api/disputes-info.md

@@ -0,0 +1,24 @@
+# Disputes Info
+
+Get information about all disputes known by the chain as well as information about which validators the disputes subsystem will accept disputes from. These disputes may be either live or concluded. The [`DisputeState`](../types/disputes.md#disputestate) can be used to determine whether the dispute still accepts votes, as well as which validators' votes may be included.
+
+```rust
+struct Dispute {
+    session: SessionIndex,
+    candidate: CandidateHash,
+    dispute_state: DisputeState,
+    local: bool,
+}
+
+struct SpamSlotsInfo {
+    max_spam_slots: u32,
+    session_spam_slots: Vec<(SessionIndex, Vec<u32>)>,
+}
+
+struct DisputesInfo {
+    disputes: Vec<Dispute>,
+    spam_slots: SpamSlotsInfo,
+}
+
+fn disputes_info() -> DisputesInfo;
+```

polkadot/roadmap/implementers-guide/src/runtime-api/known-disputes.md

@@ -1,7 +0,0 @@
-# Known Disputes
-
-Get all disputes known by the chain. These disputes may be either live or concluded. The [`DisputeState`](../types/disputes.md#disputestate) can be used to determine whether the dispute still accepts votes, as well as which validators' votes may be included.
-
-```rust
-fn known_disputes() -> Vec<(SessionIndex, CandidateHash, DisputeState)>;
-```