Update system tests, move to our latest conventions

This is a minor change that simply updates the system tests to
our latest conventions. This renames the file to match the part
of `AndSon` that we are system testing. This is our latest
convention for defining system tests. This also updates the tests
to our latest standards. Specifically this included renaming the
support `FakeServer` to `TestServer`. This is to avoid confusion
with the word "fake" in a test suite. The `TestServer` is a
`TCPServer` and processes requests. It is not a full featured
`Sanford` server. This is setup for future changes that need to
add or change system tests.
Add `before_call` and `after_call` callbacks

This adds a `before_call` and `after_call` callback that is
triggered whenever a service is called. This can be useful when
a "global" client is built and there's behavior you want to run
anytime a call is made. The callbacks are run in both live and
test clients so you get similar behavior in testing as well as
live.