custom hook to cleanly load data with an optional preview flag

compendium-frontend/src/Providers.tsx

compendium-frontend/src/helpers/PreviewProvider.tsx

compendium-frontend/src/helpers/dataconversion.tsx

compendium-frontend/src/helpers/useData.tsx

compendium-frontend/src/pages/Budget.tsx

compendium-frontend/src/pages/ChargingStructure.tsx

compendium-frontend/src/pages/CompendiumData.tsx

compendium-frontend/src/pages/ECProjects.tsx

compendium-frontend/src/pages/FundingSource.tsx

compendium-frontend/src/pages/ParentOrganisation.tsx

compendium-frontend/src/pages/Policy.tsx

compendium-frontend/src/pages/StaffGraph.tsx

compendium-frontend/src/pages/SubOrganisation.tsx