Support parameter name in CompositeEntityDefinition

[gdaniel]

DialogFlow requires to specify a parameter name for Entities references from CompositeEntities, eg.

this is a @AllInstances:Class of @Class:Class

The parameter names are provided after the ':', and allows to bind the composite values to a given name, which is useful when manipulating composite with multiple references to the same entity. The default behavior of the DialogFlowApi is to reuse the referred entity name as the parameter name, which is fine for composite entities referring only once entities. A scalable solution should allow users to specify an optional name for the parameter in case they want to create composite entities with multiple references to the same entity.

[gdaniel]

Added label Low Priority: we don't use composite entities that much