Fee Currencies - post testnet

[karlb]

See #62 for issues which are to be done before the testnet launch.

Tasks

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1. Improve logging and add metrics #74
   type:enhancement +1
   
2. Read IntrinsicGas from FeeCurrencyDirectory #125
   +0
   
3. check promoteExecutables for correctness #129
   +0
   
4. Update Info about Easy Fee Tokens / Fee Currencies for L2 docs#1325
   documentation +1
   
5. https://github.com/celo-org/celo-blockchain-planning/issues/355

P1 bugs have been moved to #185.

[piersy]

@karlb said we can probably adjust this scope to fit any timeline :D

[ezdac]

I moved the CIP-66 issue to an epic issue with sub-issue tasks #64 since it could be broken down into individual tasks for better estimation.

The individual initial time estimations are still missing there (the sum before was 120h), but I would like to wait on the input of @karlb and @carterqw2 (and whether they already came up with estimations) before putting in my own.

@lvpeschke @mcortesi