Stored conversion rate updater (#1005)

* update conversion rate: initial commit

* Rialto=Polkadot && Millau=Kusama + actually update conversion rates

* update deployment scripts and readme

* allow non-zero difference between stored and real rates

* dummy commit

* Revert "dummy commit"

This reverts commit a4381981.

* clippy

* #[allow(clippy::float_cmp)] in conversion rate update

* dummy

* Revert "dummy"

This reverts commit 90cd6e47.

* spell

* shared_value_ref() -> get()

* Revert "shared_value_ref() -> get()"

This reverts commit 20aa30de.