Improve default annotation style assignment of CAS Editor

DefaultColors.assignColors() assigns style background with somewhat random but different bright colors to all types. This method is called when is type system is not known yet.

AnnotationStyle.getAnnotationStyleFromStore() tries to read to stored style. If there is no information, then the style is set underlined red.

The situation in my use case is the following: I create a script with some type definitions resulting in a type system. I write some rules and test the result by taking a look at the xmi with the CAS Editor. Here, the first method is applied, because the type system is new. Then I write additional rules and add some other types. If I now review the result, the new types in the known types system are all set to red/underlined, because if the second method. Thus, it's harder to distinguish them.

A solution is the assignment of a random bright background color as default in AnnotationStyle.getAnnotationStyleFromStore(). However, the colors should
not change randomly if the type system changes. So after a style is assigned, this style should be stored inside the configuration, instead of repeating the process the next time the CAS is loaded. If the process is repeated and a change occurs to the type system, then the style assigning code might choose a different color.