Introduces account existence providers reference counting (#7363)

* Initial draft

* Latest changes

* Final bits.

* Fixes

* Fixes

* Test fixes

* Fix tests

* Fix babe tests

* Fix

* Fix

* Fix

* Fix

* Fix

* fix warnings in assets

* Fix UI tests

* fix line width

* Fix

* Update frame/system/src/lib.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Update frame/system/src/lib.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Fix

* fix unused warnings

* Fix

* Update frame/system/src/lib.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Update frame/system/src/lib.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Fix

* fix slash and comprehensive slash test

* fix reserved slash and comprehensive tests

* check slash on non-existent account

* Revert "Fix UI tests"

This reverts commit e0002c0f13442f7d0c95a054a6c515536328a4a0.

* Fix

* Fix utility tests

* keep dispatch error backwards compatible

* Fix

* Fix

* fix ui test

* Companion checker shouldn't be so anal.

* Fix

* Fix

* Fix

* Apply suggestions from code review

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Update frame/balances/src/lib.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* return correct slash info when failing gracefully

* fix missing import

* Update frame/system/src/lib.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Fix

* Update frame/balances/src/tests_local.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Fixes

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>
Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>
Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>