feature: Pass client configuration to `mocha.setup method.

Now all configuration in `client.config.mocha` is passed to the
setup method of mocha. The default ui style of `'bdd'` is still
set if nothing else is supplied. Also the reporter will be always
overridden as this needs to be our custom one.

Fixes #13.
Merge pull request #15 from Dignifiedquire/13_pass_client_config

feature: Pass client configuration to `mocha.setup method.