Add Token-Based Authentication

[sfkeller]

Token-Based Authentication is another method to secure web services (see also #80 for BasicAuth and NTLM). A simple implementation could be, that there is a key/value field to be filled in by the user in the service configuration. This is the parameter to be added to the http service calls. When the service call returns that the token was expired, the dialog is shown to the user and he can enter a new one.