Feature request: navigate deployments

It would be incredibly neat if it was possible to retrieve the current value of `address`-valued contract variables, and to navigate to their source code if they are also etherscan-verified contracts.

Getting the current value of all contract-level variables would also be very neat.

No files, tests, or entry points are named. Start by tracing how deployed contracts and Etherscan-verified source are currently accessed, then determine the scope for reading address-valued and other contract-level variables. Done should include retrieving the requested values and navigating verified addresses to their source.

Written by the indexing model from the issue text.