Migrate python QA tests

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Goals:

• Tests should protect the behavior guaranteed by ob-go (can be considered as acceptance or "smoke" tests)
• Tests should NOT protect derivative behavior unless the scenario can be deterministically produced (for example, asserting price calculations only when the exchange rate response can be ensured)
• Tests should cover the existing QA scenarios at minimum
• Tests should be easy to understand and expand
• Tests should be deterministic (the tests relay on the wallet API state and need to be controlled somehow: see Build Blockbook mock server multiwallet#76. Other services may need to be mocked.)
• Tests should be runnable as a suite or independently
• Stretch: Tests should be parallizable and fast.

This feature requires (hard/soft blocked by):

• Builder MVP: MVP spike mason#1 (hard blocker)
• blockbook API mocking/regtest solution: Build Blockbook mock server multiwallet#76 (hard blocker)
• Exchange rates mock: Wallet exchange rates mock data #1381 (might be able to avoid assertions specific to exchange rate)
• Search response? (unsure if search is considered in QA tests)

Related concern: #957