Offline fallback for GRANDPA (#1619)

Co-authored-by: André Silva <andre.beat@gmail.com>

* skeleton for finality tracker

* dispatch events when nothing finalized for a long time

* begin integrating finality tracker into grandpa

* add delay field to pending change

* add has_api_with function to sr_version for querying APIs

* partially integrate new force changes into grandpa

* implement forced changes

* get srml-grandpa compiling

* Update core/finality-grandpa/src/authorities.rs

Co-Authored-By: rphmeier <rphmeier@gmail.com>

* Update core/finality-grandpa/src/authorities.rs

Co-Authored-By: rphmeier <rphmeier@gmail.com>

* Update core/finality-grandpa/src/authorities.rs

Co-Authored-By: rphmeier <rphmeier@gmail.com>

* remove explicit dependence on CoreApi

* increase node runtime version

* integrate grandpa forced changes into node runtime

* add some tests to finality-tracker

* integrate finality tracking into node-runtime

* test forced-change logic

* test forced changes in the authority-set handler

* kill some unneeded bounds in client

* test forced-changes in finality-grandpa and fix logic

* build wasm and finality-tracker is no-std

* restart voter on forced change

* allow returning custom error type from lock_import_and_run

* extract out most DB logic to aux_schema and use atomic client ops

* unify authority set writing

* implement set pausing

* bump runtime version

* note on DB when we pause.

* core: grandpa: integrate forced changes with multiple pending standard changes

* core: grandpa: fix AuthoritySet tests

* runtime: bump impl_version

* core: clear pending justification requests after forced change import

* srml: finality-tracker: use FinalizedInherentData

* core: log requests for clearing justification requests

* core, node: update runtimes

* core: grandpa: fix tests

* core: grandpa: remove todos and add comments

* core: grandpa: use has_api_with from ApiExt

* core: fix tests

* core: grandpa: remove unnecessary mut modifier

* core: replace PostImportActions bitflags with struct

* core: grandpa: restrict genesis on forced authority set change

* core: grandpa: add more docs

* core: grandpa: prevent safety violations in Environment::finalize_block

* core: grandpa: register finality tracker inherent data provider

* core: grandpa: fix tests

* node: update runtime blobs

* core: grandpa: remove outdated todo

* core: aura: fix typo in log message

* core: grandpa: check re-finalization is on canonical chain

* srml: finality-tracker: fix initialization

* node: update runtime wasm

* srml: finality-tracker: don't re-initialize config keys