Unify test case & budget sharing

src/lib/components/BudgetSimulationSharingModal.svelte

src/lib/components/NavBar.svelte

src/lib/components/ShareLinkModal.svelte

src/lib/components/TestCaseSimulationSharingModal.svelte

src/lib/matomo.ts

src/lib/server/budgets.ts

src/lib/urls.ts

src/routes/+layout.svelte

src/routes/+page.svelte

src/routes/budgets/+server.ts

src/routes/budgets/demands/+server.ts

src/routes/budgets/simulations/+server.ts

src/routes/budgets/simulations/[simulation]/+page.server.ts

src/routes/simulation/+page.svelte

src/routes/simulation/+page.ts

src/routes/simulations/[simulation]/+page.server.ts

src/routes/test_cases/+server.ts

src/routes/test_cases/simulations/+server.ts

...outes/test_cases/simulations/[simulation]/+page.server.ts

src/routes/test_cases/simulations/[simulation]/+page.svelte