Extension and AddOn support

Information stems from Issue 251

verify or change the install manifest install.rdf

so that it has an ArcticFox section in

<em:targetApplication>

containing e.g.:

      <!-- Arctic Fox -->
      <Description>
        <em:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</em:id>
        <em:minVersion>45.0</em:minVersion>
        <em:maxVersion>46.*</em:maxVersion>
      </Description>

note the different em:id