Added statistics-pane & -panel to AppFrame
Added some more test-data in order to actually have statistics to
display.
Added more constructors to make adding test-data easier.
Created statistics-panel which is actually worthless and only used to
override its paint-method to provide a simple way of manual drawing with
2D-graphics.
It solely paints a small rectangle with the number of loans per date
from the first date with a loan to the current date.