Dev/bugfix

Following Issue's have been fixed with this patch:
- issue #34 JComboCheckBox NullPointerException on dropdown (OS: Windows)
- issue #30 Predefined Attributes for outputprocessors
- issue #26 Quicksave feature ist komisch
- issue #23 Undo/Redo Funktionalität unzuverlässig
- issue #16 Topography creator: esc sollte einen Zeichenvorgang abbrechen
- issue #9 Postvis: Photo und Video Export

See merge request !21

were part of the stack. This exceptions are caught in the actionPerformed method
and logged to the console on Log Level "Debug" with a simple "beep" sound for the user
to notify an empty stack

for switching back after hitting the esc key.
The Action might be initialized on two different spots. Thus in the PostvisualizationWindow
and the TopographyWindow the initialization is defined.

The Preferences.userNodeForPackage map returned the path specified with a dot at the end of the path.
Which resulted in a malformed path string without any critical effect.

To boost the usability of the Image and Video export a filechooser has been included, where the default name of the exported data fits the previously optionless default name

update migration assistent such that one can choose from based on which version a project should be reimigrated.

add migration incident to delete an element inside an array, improve the code of the Graph/Tree-class

the language should now change correctly, especially if the default language of the operating system is german.

This branch makes attributes being Cloneable.
For attributes, the default shallow clone implementation is used.
This is good as long as attributes do not have mutable sub-objects.
Note that VShape objects are not and must not be mutable.

ScenarioElements implement a clone method. Implementations use a
constructor and pass cloned attributes. ScenarioElements are not
Cloneable because they do not user super.clone() which makes a shallow
copy.