Allow DeckEntrances on Deck and deprecate deckEntranceCouples

[Robbendebiene]

Partially resolves: #702

xsd/netex_framework/netex_reusableComponents/netex_deckPlan_version.xsd
As a DeckEntrance can be referred to from two DeckSpaces I think it should be possible to (also) define them (but not refer them) at DECK level (i.e. in DeckGroup) and not only inside a certain DeckSpace. That means a profile could then require them to be defined at DECK level and forbid that they are defined inside a DeckSpace. Thus always using references (e.g. DeckEntranceRef) inside DeskSpaces.

xsd/netex_framework/netex_reusableComponents/netex_deckPlan_version.xsd

deckEntranceCouples should not be allowed to be defined within a certain DeckSpace as it always refers to two deckEntrances on the same DECK. Instead it should be defined on DECK level. Thus move deckEntranceCouples from DescSpaceEntranceGroup to DeckGroup

In contrast to the above suggestion this deprecates deckEntranceCouples as proposed here: https://3.basecamp.com/4847067/buckets/19640795/messages/8724984447

Initially I wanted to keep the idea of coupling for different carriages by adding refs to the TrainComponentCouplingStructure (see code below). However this still doesn't allow the coupling of 2 carriage entrances with the same DeckPlan so I did not do it. Coupling between DeckEntrances marked as communicating can still be done implicitly based on their VehicleSide and the order + details of the respective TrainComponents.

Discarded idea for explicit coupling of DeckEntrances from different DeckPlans

<xsd:complexType name="TrainComponentCouplingStructure">
	<xsd:annotation>
		<xsd:documentation>Type for a TRAIN COMPONENT COUPLING.</xsd:documentation>
	</xsd:annotation>
	<xsd:sequence>
		<xsd:element name="Splittable" type="xsd:boolean" minOccurs="0">
			<xsd:annotation>
				<xsd:documentation>Whether the component can be split in normal usage.</xsd:documentation>
			</xsd:annotation>
		</xsd:element>
		<xsd:element name="ThroughAccess" type="ThroughAccessEnumeration">
			<xsd:annotation>
				<xsd:documentation>Whether passenger can walk through coupling to next carriage.</xsd:documentation>
			</xsd:annotation>
		</xsd:element>
		<xsd:sequence minOccurs="0">
			<xsd:element name="FromDeckEntranceRef" type="DeckEntranceRefStructure" minOccurs="1">
				<xsd:annotation>
					<xsd:documentation>Communicating DECK ENTRANCE of this TRAIN COMPONENT's DECK PLAN that links to a communicating DECK ENTRANCE of other TRAIN COMPONENT's DECK PLAN.</xsd:documentation>
				</xsd:annotation>
			</xsd:element>
			<xsd:element name="ToDeckEntranceRef" type="DeckEntranceRefStructure"  minOccurs="1">
				<xsd:annotation>
					<xsd:documentation>Communicating DECK ENTRANCE of other TRAIN COMPONENT's DECK PLAN that links to a communicating DECK ENTRANCE of this TRAIN COMPONENT's DECK PLAN.</xsd:documentation>
				</xsd:annotation>
			</xsd:element>
		</xsd:sequence>
	</xsd:sequence>
</xsd:complexType>