EIP 1559 introductory support

[wolovim]

What was wrong?

Etheriom keeps updating.

(Related to #1835)

How was it fixed?

This is early, exploratory code:

• wrote some test cases (probably not comprehensive)
• parsed out legacy vs. 1559 txs in the gas_price_strategy_middleware
• pulled latest Geth from master & built from source London now available in Geth v1.10.4
• generated a London test fixture from Geth v1.10.4 (common_1559.py is temporary for this purpose)
• ran the integration test suite through the new fixture to see what explodes

Todo:

• input munging
• revisit gas price generation
• debug a couple failing tests
• update docs for sending txs (maxFeePerGas & maxPriorityFeePerGas)
• update docs for retrieving blocks (baseFeePerGas)
• Add entry to the release notes

Cute Animal Picture

[wolovim]

Theoretically London goes live on Ropsten tomorrow, so its about time to get this work off my fork and into a Web3.py branch for easier use on testnets. Once this is up on a branch, I can remove myself as the gatekeeper and anyone can create PRs against it. I've created a london branch, and this PR now points at it.

Current state:

• Core functionality is there and ready for testnet testing. There's an edge case or two that needs a design decision or polish.
• There are a couple of grumpy tests that we still need to track down; I don't believe their failures indicate anything mission critical, but rather some fine tuning that needs to happen/cleanup where some tests are polluting the context of those failing tests.
• One of the bigger TODOs: gas price generation code needs a hard look. A naive version may be the short term solution, until 'smarter' ones are figured out, e.g., something involving feeHistory.

[kclowes]

LGTM for branch merge! Just left one question 🚀