Added DbWrapperTest.java.

Slightly diverted scheme_setup.sql (changed some inserts).

DbWrapper: Added several methods for conversion, some predicates and an own errorMessageBox.

BirdwatcherRepository: Refactored code of isRegistered().

MerlinLogin: Edited FocusTraversalOnArray stuff. Still throws errors like hell...

MerlinMainWindow: Added windowClosing to listen for any closing promts to the main window (will prompt the user to decided wheter the program should be terminated or not).
Merge branch 'master' of https://github.com/Isaisaisa/DB-Merlin
Merge branch 'master' of https://github.com/Isaisaisa/DB-Merlin

Conflicts:
	Aufgabe_3/src/merlin/gui/MerlinMainWindow.java