WebRequestor methods refactoring

[nbartels]

With the access token as header field change, we had to add this String as additional parameter and this made the method signatures less structured. So we have to change this and provide a new WebRequestor.Request object that encapsulates all the possible parameters and provides some convenience methods to move some logic away from the DefaultWebRequestor.

This will improve the complexity and methods with less parameters are better ;)

But this is a breaking change as soon as you have a custom WebRequestor with your own executePost|Get|Delete methods.