Stored call in multisig (#6319)

* Stored call in multisig

* Docs.

* Benchmarks.

* Fix

* Update frame/multisig/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* patch benchmarks

* Minor grumbles.

* Update as_multi weight

* Fixes and refactoring.

* Split out threshold=1 and opaquify Call.

* Compiles, tests pass, weights are broken

* Update benchmarks, add working tests

* Add benchmark to threshold 1, add event too

* suppress warning for now

* @xlc improvment nit

* Update weight and tests

* Test for weight check

* Fix line width

* one more line width error

* Apply suggestions from code review

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

* fix merge

* more @apopiak feedback

* Multisig handles no preimage

* Optimize return weight after dispatch

* Error on failed deposit.

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>