- ComboBoxEditingSupport / value providers

  - Enable selection of values for non-enum attributes from a combo box. The following options are available:
    - Fix set of values
    - Dynamically managed set of values. The user may either choose from the existing values for a given annotation type, or enter a new one. Deleting existing choices is also supported.
  
- AnnotationViewPartBase: Also watch specifications in order to ensure update of admissible choices (see code for detailed comments)

- GenericAnnotationView: Set viewer input before construction of columns in order to enable aggregation of admissible values
refs 1841