Migration to planetary coverage package

• Upgrade to planetary-coverage==1.0.0
• Replace all moon-coverage references to planetary-coverage in the text
• Replace all the url links to the new locations (docs/juigitlab/pypi/nbviewer/binder)
• Replace README illustration
• Fix Europa links and imports
• Add support for .env file and %load_ext planetary_coverage in spice_kernels.ipynb
• Add support for load_kernels=True example in spice_kernels.ipynb
• Add support for .orb file reader in esa_events.ipynb
• Add support for EventWindow trimming at boundary conditions in esa_events.ipynb
• Add solar system example (8-solar_system) with plot on Mars surface with planetographic coordinate plot and PNG display and west_ticks