CheckReports, CheckUser, ConfirmReplies, ConfirmReports, DeleteScheduledMessages, FaultResponse

In order to complete this project on time, I've decided to open this pull request even though the old one is not yet merged into master. Please excuse the old comments that will probably show up here as well.

It includes all Requests & Responses mentioned above.

I'm still having troubles testing some requests & responses since I need the message IDs from send messages for them. (compare the end of sms_interface_spec.rb.)
They do work as expected, I just can't test them right now.

I'll look into a way to do that. So for the moment this pull request is not ready. But please do comment on anything you don't like.