Move/copy runtime-common to fellowship repo

[gpestana]

Some of the implementations under polkadot-sdk's polkadot-runtime-common crate are critical to Polkadot and Kusama (e.g. fn era_payout, which implements the inflation formula). This logic should probably be under the umbrella of the fellowship. Since the westend and rococo runtimes also need the runtime-common, another option is to keep a different runtime-common crate in each repo.

[bkchr]

Yeah this requires some kind of clean-up. We probably should start by moving out the crates from runtime-common in the Parity repos. Then having a copy of this crate should be fine.

[joepetrowski]

Should also include #109 (comment)

[bkontur]

relates to: paritytech/polkadot-sdk#3054