Adds lots of page stubs

config.yml

content/PlanetarySDIs/_index.md

content/PlanetarySDIs/about.md

content/europa/about.md

content/europa/data/_index.md

content/europa/data/data_gaps.md

content/europa/data/data_products.md

content/europa/data/data_services.md

content/europa/get_involved.md

content/europa/governance.md

content/europa/governance/_index.md

content/europa/governance/acknowledgements.md

content/europa/governance/charter.md

content/europa/governance/data_standards.md

content/europa/governance/governance_model.md

content/europa/governance/intro.md

content/europa/governance/recurring_agenda.md

content/europa/governance/standards.md

content/europa/governance/working_group.md

content/europa/meeting_notes/_index.md