The work includes the reactor which ties together all the seperate routines involved in the design of the blockchain v2 refactor. This PR replaces #4067 which got far too large and messy after a failed attempt to rebase.

## Commits:

* Blockchainv 2 reactor:

	+ I cleaner copy of the work done in #4067 which fell too far behind and was a nightmare to rebase.
	+ The work includes the reactor which ties together all the seperate routines involved in the design of the blockchain v2 refactor.

* fixes after merge

* reorder iIO interface methodset

* change iO -> IO

* panic before send nil block

* rename switchToConsensus -> trySwitchToConsensus

* rename tdState -> tmState

* Update blockchain/v2/reactor.go

Co-Authored-By: Bot from GolangCI <42910462+golangcibot@users.noreply.github.com>

* remove peer when it sends a block unsolicited

* check for not ready in markReceived

* fix error

* fix the pcFinished event

* typo fix

* add documentation for processor fields

* simplify time.Since

* try and make the linter happy

* some doc updates

* fix channel diagram

* Update adr-043-blockchain-riri-org.md

* panic on nil switch

* liting fixes

* account for nil block in bBlockResponseMessage

* panic on duplicate block enqueued by processor

* linting

* goimport reactor_test.go

Co-authored-by: Bot from GolangCI <42910462+golangcibot@users.noreply.github.com>
Co-authored-by: Anca Zamfir <ancazamfir@users.noreply.github.com>
Co-authored-by: Marko <marbar3778@yahoo.com>
Co-authored-by: Anton Kaliaev <anton.kalyaev@gmail.com>