This way the logs do not interfere with test output

Handler Chain is  of handlers that respond to call.
Invoking handle(*args) on the chain will call the handlers with the given args
until one of them returns a result that is truethy (i.e. not false or nil).

Extracted from the dispatcher so we can also handle exceptions there in the
future. (So that if one of the network connections to the request_handlers
fails we can continue while still tracking the failed exception.)

This is a first step. In case the suspected nicknym server cannot be
reached we will now move on and try other sources.

It's robably not what we want in the long run. In order to know wether
no key exists or we just failed to connect to some servers a different
http response code would be nice if network errors occured.

This simplifies testing such scenarios in the unit test and makes the
remote tests skip on network failure.

Dropped the webmock dependency. We have our own http adapter. So we can
stub that to inject a mock. As an added bonus this does not mess with
other http requests.

Also wrote down testing strategy. Not completely implemented yet.

Also changed Nickserver::Response to not include the status code.
This may be okay for error responses but in most cases we want to
have a parsable message and not some status code prepended to it.

I added a RequestHandler that uses Nicknym::Source - but that has not
been implemented yet.