Allow to pass the `adapter` option in globals, pass it to HTTPI when performing SOAP calls.

It will be useful for those people who need to use different HTTPI adapters for different services, see #564

I don't know, how to test this, please tell me any ideas and suggestions, I'll write tests and append it to this request.

Closes #564
Requires savonrb/wasabi#44 to be merged in and published with version bump (included).