Fix weight accounting (!246)

* remove impl-for-tuples

* update metadata

* remove unused benchmark

* update weights

* simplify weight accounting

* revert weight addition

* add docs for handlers

* unify handlers implementation in runtime

* remove weight accounting OnNewIdty

* simplify IdtyChange handlers

* add handlers documentation

* simplify Membership handlers

* split OnEvent membership handler

* fix formatting

* fix weight for tuple handler

* add weight for on_removed_wot_member