CSE: support aliases for contract fields

We should add NatSpec annotations that allow to indicate that contract fields correspond to the same contract/account, e.g. /// @custom-kontrol-alias: escrowOne.oneEth, escrowTwo.oneEth,. They could then be used when CSEing contracts such as Governance:

contract Governance {
   OneEth oneEth;
   EscrowOne escrowOne;
   EscrowTwo escrowTwo;
   ...
}

contract EscrowOne {
   OneEth oneEth;
   ...
}

contract EscrowTwo {
   OneEth oneEth;
   ...
}

in order to only generate a single account for oneEth instead of three (one for each contract involved).

The issue names no files or tests; start by locating Kontrol's NatSpec/custom-annotation parsing and the CSE entry point for contract fields. Trace how Governance's escrowOne, escrowTwo, and oneEth fields become accounts, then define and test the alias behavior so the annotated fields produce one account rather than three.