Add + test a `StorageSetter` contract that can be
used by upgrades and storage migrations. This contract
exists to decouple migrations from implementations.
The existing contracts use `Initialize` which is a leaky
abstraction because it includes the fact that the implementation
is behind a proxy in the implementation code itself.
The logic in `initialize` must include logic that can
ensure the storage is correct for any version upgrading
to any version as well as going from empty storage for
new deployments, adding a lot of complexity. This contract
should be used as an intermediate step in upgrades, so that
this contract can be used to migrate storage between
different implementations.