Add MessageBox to UserConsent (issue #180)

This includes the MessageBox-Interface, a full swing implementation of this interface and a basic
android implementation supporting only simple message boxes with a OK button.
Factor out Options, Dialog and Result type, and corrections in the interface (issue #180)
Refinement of message box (issue #180)

Remove default title and change options parameters. Replace "Box" with "Dialog" in MessageBox
classes and functions and simplify ResultType.