#283 added a unit test to check action tags

The unit test fails at the moment, because if different action tags are checked
from different threads, the wrong result might be returned.
 #283 load the restriction color in a worker

The color for the Sb_stadtbildserieGridObjects are loaded in a
SwingWorker as they freeze the GUI. To handle the fetched objects better
a BulletPointSettings class was introduced.
 #283 keep the ratio of images while scaling

To keep the ratio while scaling images, the image is first scaled and
then the center is cropped with the right size.
Merge branch 'feature/283-changes-in-StadtbildserienAggregationRenderer' into dev