feat: adds direct mode verification agent

[kentbull]

This adds a VerificationAgent that handles the CESR streams fed to the parser from the HttpEnd at the / base route. This allows for PUTs of CESR streams to send ACDC presentations to the VerificationAgent. This supports AIDs that do not have any witnesses because rather than using a mailbox to receive messages then the VerificationAgent is always on and receives CESR streams directly at /.

CESR streams go from:

- HTTP Request 
  -> HttpEnd 
    - > Parser.ims 
      - > one of Kevery (KEL evt), Tevery (TEL evt), Revery (), Exchanger (exn), or Verifier (ACDCs) 
        - > appropriate LMDB database class 
          - > VerificationAgent to be processed by its escrows

[kentbull]

This PR does not remove the indirect mode mailbox listener, which is still the default way to run Sally. It uses the new --direct flag to turn on direct mode.