* pre_upgrade hook wip

* working pre_upgrade

* simplify code

* cleanup and document

* return reads from get_account_deposited_and_staked_sums

* improve comment

* on_runtime_upgrade comment

* post upgrade comment

* use saturating_add

* clippy

* clean up balances

* add tests

* fix comment

* oops

* actually fix comment

* fix std build

* address pr comments

* remove redundant comment

* update comment

* add comment

* oliver comments from tips pallet pr

* lint

* remove need for do_pre/do_post runtime functions

* generic dbweight

* Update frame/elections-phragmen/src/migrations/unlock_and_unreserve_all_funds.rs

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* Update frame/elections-phragmen/src/migrations/unlock_and_unreserve_all_funds.rs

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* pr comments

* remove useless check

* feature gate log target

* lint

* Update frame/elections-phragmen/src/migrations/unlock_and_unreserve_all_funds.rs

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* add log for unexpected amounts

---------

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>