eth,misc: Use transaction manager with confirmation and optional replacement queue

[kyriediculous]

What does this pull request do? Explain your changes. (required)
Use a TransactionManager to handle transactions. This service will forward transactions to the ethereum JSON-RPC, when a transaction is broadcasted to the ethereum network it will be added to the queue. Lowest non-confirmed transactions are popped off the queue to wait until they are mined and retrieve their transaction receipt.

Once the transaction receipt is found it will be sent over a subscription of transaction receipts that services that want feedback on tx confirmation can subscribe to. This subscription service now powers LivepeerEthClient.CheckTx() under the hood.

Specific updates (required)

• 75eed97 eth: transaction manager with confirmation queue and optional replacement transactions

• 60d33a0 pm: handle ticket revert error

• a7b7c5e eth: remove replacement transactions from reward service

• d4886f6 eth,server: move max gas price logic to gas price monitor

• b12a24d eth: make abiMap and txLog helpers in the eth package rather than Backend methods

• 1b89b5c cmd: replace transaction flag

• efa84b4 cmd,eth: use struct for LivepeerEthClient constructor parameters that aren't other services

How did you test each of these updates (required)

• Unit tests

• TODO add TransactionManager unit tests

Does this pull request close any open issues?
Fixes #1906

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[kyriediculous]

@yondonfu Do we want persistent storage for the transaction confirmation queue to avoid unexpected behaviour between node restarts when transactions are still pending ?

[yondonfu]

How were these changes tested?

Given that the logic of the transaction manager for handling replacing pending transactions is important for funds management and node operation could we add unit tests particularly around the automated transaction replacement flow?

[yondonfu]

Just two comments to address:

• Default flag values
• Small test related comment

Let's also rebase on top of master to resolve the conflicts. Feel free to do this in conjunction with addressing the remaining comments.

[kyriediculous]

Rebased, resolved merge conflicts and addresses the remaining changes.

Also moved min and max gas price completely into GasPriceMonitor as discussed previously.

[yondonfu]

LGTM after squashing 🚢