Add Update to NetworkLinkControl

[cleder]

Follow up to #390, blocks #317

Add missing update functionality to NetworkLinkControl with the Delete, Create and Change objects:

<NetworkLinkControl>      
      <Update>
        <targetHref>http://barcelona.galdos.local/svn1/sqa/ets-kml/main/test/data/ogc-kml/files/ge_.kmz</targetHref>
        <Delete>
          <PhotoOverlay targetId="id_550e8400-e29b-41d4-a716-446655440000" />
        </Delete>
        <Create>
          <Folder targetId="Folder-001">
			<name>Mauris vulputate pulvinar.</name>
          </Folder>
        </Create>
        <Change>
          <TimeSpan targetId="id_f272fc30-185d-11dd-bd0b-0800200c9a66">
            <begin>2008-03-15T00:00:00Z</begin>
            <end>2008-03-29T00:00:00Z</end>
          </TimeSpan>
        </Change>
      </Update>
    </NetworkLinkControl>

Syntax

<Update>
  <targetHref>...</targetHref>    <!-- URL -->
  <Change>...</Change>
  <Create>...</Create>
  <Delete>...</Delete>
</Update>

Description Specifies an addition, change, or deletion to KML data that has already been loaded using the specified URL. The <targetHref> specifies the .kml or .kmz file whose data (within Google Earth) is to be modified. <Update> is always contained in a NetworkLinkControl. Furthermore, the file containing the NetworkLinkControl must have been loaded by a NetworkLink. See the "Topics in KML" page on Updates for a detailed example of how Update works.

Elements Specific to Update Can contain any number of <Change>, <Create>, and <Delete> elements, which will be processed in order.

https://developers.google.com/kml/documentation/kmlreference#example-of-change

<Update>
  <targetHref>...</targetHref>    <!-- URL -->
  <Change>...</Change>
  <Create>...</Create>
  <Delete>...</Delete>
</Update>

https://developers.google.com/kml/documentation/kmlreference#example-of-create https://developers.google.com/kml/documentation/kmlreference#example-of-delete