Added a way to define macro property features as mandatory with the `@PropertyFeature` annotation

The @PropertyFeature annotation used to define the feature of a property, typically used in java Macro parameter definitions, now supports a mandatory attribute. A mandatory feature is a feature for which at least one field fulfilling this feature must have a value. E.g. The reference feature of the include macro is implemented by two properties: reference and page. Making the feature mandatory with:

@PropertyFeature(value = "reference", mandatory = true)

Means that at least one of the properties reference or page MUST have a value for the provided macro parameters to be valid. This is an intermediate level between making both properties mandatory and having no mandatory property.