- GSNPositionedEditPartBase*: Avoid code duplication by pushing refreshDecorationFigure() to PositionedEditPartBase
- PositionedEditPartBase.refreshDecorationFigure()
  - Avoid SWT Image leak by reusing the same icons
  - Add more null-checks to implementation
- MarkerViewPart -> column updater: Avoid SWT Image leak by disposing old image before setting a new one

- Undo last two changes: will be handled by ElementCompositorService (in the kernel)

refs 2309

refs 2309

- Assign unique IDs to annotations as soon as the are instantiated (before, annotations relied on the ID-fixup that is triggered when the model is persisted)
refs 2309

- Keep order of elements to be selected (e.g., EENum values) etc. by using a LinkedHashMap instead of a TreeMap

Fixes a bug in the EStructuralFeatureValueProvider that caused the Enum filter list to be applied on objects that should not be filtered.

Adds the possibility to filter the list of available choices for an enum-type annotation via the annotation's value provider.
Therefore, a map containing the class of the to be filtered model elements and the allowed enum literal must be given in the constructor of the value provider.

DerivedAnnotationValueProviderBase.setAnnotationValue(): Convert String-encoded input to actual data type

refs 2240

refs 2226

refs 2289

generalize RequirementSpecificationUtils.removeRequirementSpecifications() to 
BaseModelElementUtils.removeModelElementReferenceSpecifications()
  
refs 2240

refs 2140

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255

refs 2255