#79 small geometries are now also visible

Created a small heuristic to make small geometries also visible in the
preview.
 #79 created PreviewMapPanel

PreviewMapPanel is a panel which contains a mapping component and can
show a geometry of a CidsBean.
 #79 moved the map to PreviewMapPanel

Moved the implementation from GeometryChooserPanel to PreviewMapPanel,
thus only one class implements initMap()
Merge branch 'bug/79-small-preview-for-small-geometries' into dev