Patch solc 0 5 0

[rob-Hitchens]

Refactor solidity contracts/examples so they compile with solc 0.5.0.

[knkski]

@rob-Hitchens: Thanks for your PR! It looks like you'll need to add a DCO signoff in your commit message (see https://sawtooth.hyperledger.org/docs/core/nightly/master/community/contributing.html#the-commit-process for more details).

Also, has the bytecode for any of the contracts changed? The corresponding *.txt files alongside the *.sol files might need updating (see https://sawtooth.hyperledger.org/docs/seth/releases/latest/contracts.html for info on how to compile contracts).

[vaporos]

Closing due to lack of DCO. Please address and re-open this PR.