New features

* Added SoapAppClient which works with an AppConnector. (The other clients are dysfunctional since 2017-01-01, when AFAS shut off NTLM authentication.)
* Reorganized code between the Connection and Client classes so that they are now independent. (All call arguments used to be handled in the Connection class; that became quite messy. The authentication related arguments are now only known by the Client which is a much cleaner distinction.
* Moved all error reporting stuff out of the classes; they throw Exceptions now. (Error reporting is back in the .module for now.)