ABI Interaction integration tests with app calls

[algochoi]

This PR introduces some Cucumber integration tests for interacting with ARC-0004 compliant apps using the AtomicTransactionComposer in the SDKs.

PyTeal contract: gist

This change is composed of:

1. Payment transaction unit tests
2. Composer unit tests that build and sign the transaction, and compares the signed transactions to a golden
3. Composer integration tests that build, clone, sign, and executes the transactions and compares the logged results to the expected values.

Closes #146

Todo:

• Standardize how return logs are handled (Hash the word return)

[jasonpaulos]

This appears to test AtomicTransactionComposer in a more indirect way than what I was expecting. I was imagining we would have new steps for each action of the composer and mix these in with some of the existing transaction construction steps. Something like:

Given a new atomic transaction composer
And suggested transaction parameters fee <fee>, flat-fee "<flat-fee>", first-valid <first-valid>, last-valid <last-valid>, genesis-hash "<genesis-hash>", genesis-id "<genesis-id>"
When I build a transaction ...
And I make a transaction signer for account mnemonic "<mnemonic>"
And I add the transaction and signer to the composer
And I gather signatures with the composer
Then the signatures should equal "<expected>"

Though admittedly we only have general txn construction steps for app and keyreg txns at the moment. If needed I can help flesh these out for the other txn types.

I may have lead you astray by suggesting we reuse steps as much as possible. In general we should do that, but it doesn't appear to apply to this test very much.

[algochoi]

I only added a PaymentTxn test case for now since the current tests only require payments -- I can create a ticket for creating the remaining transaction types in the cucumber tests.

[algochoi]

Split up the tests so the unit tests check for the signed transaction goldens and the integration tests check for the app return values.

One tricky thing is how we build up transaction and app arguments for the method calls, and I've just chosen to hard-code it on the Cucumber side rather than the SDK side. It would be nicer if the transactions can be "parameterized" better, but I'm not sure if there is a better way right now.

[algochoi]

I updated the tests and tested them against the Python SDK. This commit contains the relevant diff for implementing the test steps in the Python SDK: algorand/py-algorand-sdk@e96b740

[jasonpaulos]

Looks good!