EWS: Refactor server connection and password retrieval
In the old behaviour the resource would attempt to connect to the server at resource construction time, which is not the way it should work. This was a corner cut done in early development, when I was still a novice and I wanted it to just work. As we know cutting corners tends to backfire eventually... The updated implementation connects to the server when the resource is brought online. The password request code also received refactoring. Instead of synchronously waiting for KWallet it now performs the opening asynchronously together with a timeout for safety. A new unit test ensures that the code behaves as designed.