Generalised proxies (#6156)

* Initial work

* It should work

* Fix node

* Fix tests

* Initial test

* Tests

* Expunge proxy functionality from democracy and elections

* Allow different proxy types

* Repotted

* Build

* Build

* Making a start on weights

* Undo breaking change

* Line widths.

* Fix

* fix tests

* finish benchmarks?

* Storage name!

* Utility -> Proxy

* proxy weight

* add proxy weight

* remove weights

* Update transfer constraint

* Again, fix constraints

* Fix negation

* Update frame/proxy/Cargo.toml

Co-authored-by: Kian Paimani <[email protected]>

* Remove unneeded event.

* Grumbles

* Apply suggestions from code review

Co-authored-by: Kian Paimani <[email protected]>

Co-authored-by: Shawn Tabrizi <[email protected]>
Co-authored-by: Kian Paimani <[email protected]>