implement fallback on defaultValue
remove duplicated if-statement
removed obsolete code
an abstract IFilter that can be run on any AttributeDefinition

the operators IS_SET and IS_NOT do not depend on the type of the
attributeDefinition
define SUPPORTED_OPERATORS in AbstractAttributeFilter
refactored filters to extend AbstractAttributesFilter
Refactoring of Enum selector to be usable independent from AgileGrid.
Better label for enum selector.