Remove gml:AssociationAttributeGroup from appearance property type

[clausnagel]

The <core:appearance> property element of core:AbstractCityObjectType is currently defined such that it can carry the Appearance inline or reference it using an XLink.

Sharing appearances between city objects this way does not make much sense in my opinion. An inline property seems to be more appropriate. This might also be true for other feature properties that are strongly related to a specific city object (e.g. core:dynamizer).

[clausnagel]

For example, I think that core:CityObjectRelationPropertyType should also be changed into an inline property. Why should a relation between feature A and B be referenced and reused by feature C?

More properties and property types:

• volume of core:AbstractSpaceType
• area of core:AbstractSpaceType
• area of core:AbstractThematicSurfaceType
• core:ImplicitGeometryPropertyType
• ...Member of core:CityModelType
• roomHeight of bldg:BuildingRoomType (note that AbstractConstructionType uses HeightPropertyType which is an inline property...)