Add EnumSetProperty

[ljacqu]

Introduce an EnumSetProperty that goes along with EnumSetPropertyType.

To do

• Create a class EnumSetProperty in the same package as SetProperty
  • It should extend SetProperty and use the constructor that takes PropertyType<Set<E>> as argument
  • Call the constructor with the already existing EnumSetPropertyType
  • Expected constuctors on EnumSetProperty are EnumSetProperty(String path, Class<E> enumClass, E... defaultValue) and EnumSetProperty(String path, Class<E> enumClass, EnumSet<E> defaultValue)
• Add tests (see other test classes, like LowercaseStringSetPropertyTest)