support option for no-root-of-trust / skipping validation of signatures

[willscott]

when the remote web3 gateway supports the web3c protocol, but is running in a test or insecure mode where a trusted key manager is not running, it won't be able to produce valid signatures.

We should allow the client library to be instantiated in an insecure mode where it skips validation of signatures, similar to the path already implemented for testing, such that protocol functionality can be tested in insecure instances.