Add ExoMars TGO CaSSIS ingestion program and mission files to ISIS
This will have no impact on existing ISIS programs.
ExoMars Trace Gas Orbiter CaSSIS images will be ingested into ISIS cubes. SPICE should be added to the data area and mission support documentation will be added to the ISIS website documentation.
In order to do this, we will also need to update the current PVL translation file format to be able to translate from XML labels.