Fix enumeration in wingWingAttachmentType

[MarAlder]

The upperShellAttachment and lowerShellAttachment elements in wingWingAttachmentType must not be of stringUIDBaseType, but an enumeration of upperShell and lowerShell.

[MarAlder]

Imlemented

<xsd:complexType name="wingWingAttachmentType">
        <xsd:annotation>
            <xsd:appinfo>
                <sd:schemaDoc>
                    <ddue:summary>
                        <ddue:para>wingWingAttachmentType</ddue:para>
                    </ddue:summary>
                    <ddue:remarks>
                        <ddue:para>Definition of the structural connection between two
                            wings resp. two componentSegments. Note: All structural
                            connections between two wings/componetSegments have to be defined
                            using wingWingAttachments. The wingWingAttachment has only be
                            defined in one of the two componentSegments, that are connected.
                        </ddue:para>
                    </ddue:remarks>
                </sd:schemaDoc>
            </xsd:appinfo>
        </xsd:annotation>
        <xsd:complexContent>
            <xsd:extension base="complexBaseType">
                <xsd:all>
                    <xsd:element name="toComponentSegmentUID" type="stringUIDBaseType">
                        <xsd:annotation>
                            <xsd:documentation>UID of the componentSegment, that is connected
                                with the current one.</xsd:documentation>
                        </xsd:annotation>
                    </xsd:element>
                    <xsd:element name="elements" type="wingWingAttachmentElementsType"/>
                    <xsd:element name="sparAttachments" type="wingWingAttachmentsSparsType"/>
                    <xsd:element name="upperShellAttachment">
                        <xsd:annotation>
                            <xsd:documentation>Defines if the upper shell of the current
                                componentSegment is structurally connected to the upper or lower
                                shell of the second componentSegment. Can have the values
                                'upperShell' or 'lowerShell'.</xsd:documentation>
                        </xsd:annotation>
                            <xsd:complexType>
                            <xsd:simpleContent>
                                <xsd:restriction base="stringBaseType">
                                    <xsd:enumeration value="upperShell"/>
                                    <xsd:enumeration value="lowerShell"/>
                                </xsd:restriction>
                            </xsd:simpleContent>
                        </xsd:complexType>
                    </xsd:element>
                    <xsd:element name="lowerShellAttachment">
                        <xsd:annotation>
                            <xsd:documentation>Defines if the lower shell of the current
                                componentSegment is structurally connected to the upper or lower
                                shell of the second componentSegment. Can have the values
                                'upperShell' or 'lowerShell'.</xsd:documentation>
                        </xsd:annotation>
                            <xsd:complexType>
                            <xsd:simpleContent>
                                <xsd:restriction base="stringBaseType">
                                    <xsd:enumeration value="upperShell"/>
                                    <xsd:enumeration value="lowerShell"/>
                                </xsd:restriction>
                            </xsd:simpleContent>
                        </xsd:complexType>
                    </xsd:element>
                </xsd:all>
            </xsd:extension>
        </xsd:complexContent>
    </xsd:complexType>