Warn about "unresolved calls" and add option to prevent speculative method attribution

[cgewecke]

Sometimes the reporter is unable to resolve the contract target of a method call. These occurrences are tracked but we don't currently warn about them...

Additionally, the reporter falls back on matching transactions by function signature alone, potentially corrupting data in projects where method sigs shadow each other. This is convenient for cases where solc's deployedBytecode doesn't match the code on-chain but the behavior definitely shouldn't be silent.

We should

• warn about unresolved calls
• have an option to turn "guessing" (e.g fnSig matching) off