Extend capType with uID attribute

[sdeinert]

In order to improve identification of structural caps and posts using the capType this type should be extended with an (optional) attribute for a uID:

<xsd:complexType name="capType">
    <xsd:annotation>
        <xsd:appinfo>
            <sd:schemaDoc>
                <ddue:summary>
                    <ddue:para>capType</ddue:para>
                </ddue:summary>
                <ddue:remarks>
                    <ddue:content>
                        <ddue:para>SparCap type, containing the cross section area of the
                            spar cap and the material properties.</ddue:para>
                        <ddue:para>Pleas find below a picture where all spar cross
                            section parameters as well as the orientation refereneces for
                            the material definition can be found:</ddue:para>
                        <ddue:mediaLink>
                            <ddue:image xlink:href="spars2"/>
                        </ddue:mediaLink>
                    </ddue:content>
                </ddue:remarks>
            </sd:schemaDoc>
        </xsd:appinfo>
    </xsd:annotation>
    <xsd:complexContent>
        <xsd:extension base="complexBaseType">
            <xsd:sequence>
                <xsd:element name="area" type="doubleBaseType">
                    <xsd:annotation>
                        <xsd:documentation>Area of the cap.</xsd:documentation>
                    </xsd:annotation>
                </xsd:element>
                <xsd:element name="material" type="materialDefinitionType">
                    <xsd:annotation>
                        <xsd:documentation>Material properties.</xsd:documentation>
                    </xsd:annotation>
                </xsd:element>
            </xsd:sequence>
            <xsd:attribute name="uID" type="xsd:string"/>
        </xsd:extension>
    </xsd:complexContent>
</xsd:complexType>