Fix simple policy implementation for outgoing transactions

[jseagrave21]

What current issue(s) does this address, or what feature is it adding? Addresses #960; specifically, https://github.com/CityOfZion/neo-python/issues/960#issuecomment-512248474

How did you solve this problem? implement SimplePolicy check when relaying any tx

• results in a cancelled tx and a required fee recommendation if SimplePolicy requirements are not met
• addresses https://github.com/CityOfZion/neo-python/issues/960#issuecomment-512248474 by checking each tx after it is signed

How did you make sure your solution works? make test with unittests

Are there any special changes in the code that we should be aware of? Replaced TXFeeError with TXError to incorporate a check for violating the tx maximum size

Please check the following, if applicable:

• [x] Did you add any tests?
• [x] Did you run make lint?
• [x] Did you run make test?
• [x] Are you making a PR to a feature branch or development rather than master?
• [x] Did you add an entry to CHANGELOG.rst? (if not, please do)

[coveralls]

Coverage increased (+0.003%) to 85.266% when pulling 5e65d840132f71efc6b956fe543a4e4b3ddcb9ae on jseagrave21:fix-SimplePolicy into 36c2860488311a827898a9cd636467c5eaccb711 on CityOfZion:development.

[ixje]

note to self; gave slack feedback regarding late notification if funds are insufficient

[ixje]

I had another look at the code because it just didn't feel right to have relay() be responsible for policy validation. One of the issues in resolving this in the best way possible is that certain code parts do too much e.g. https://github.com/CityOfZion/neo-python/blob/fe90f62e123d720d4281c79af0598d9df9e776fb/neo/Prompt/Commands/Invoke.py#L48

does not just invoke a contract, it also sign's the TX and this is a problem for reporting the required fees prior to asking if the TX should be send to the network. Instead of resolving the latter now I want to keep that in mind for the NEO3 build.

I moved the policy validation into its own function and out of the relay() code because those 2 should not be tied together. In doing so I could also simplify some of the test logic.

[ixje]

🎉