Move development pages to their own directory.

src/lib/components/DevNavBar.svelte

src/lib/components/NavBar.svelte

src/routes/dev.svelte

src/routes/dev/__layout.reset.svelte

src/routes/dev/calculations.svelte

src/routes/dev/entities.svelte

src/routes/dev/index.svelte

src/routes/dev/parameters/[parameter].svelte

src/routes/dev/parameters/index.svelte

src/routes/dev/variables/[variable]/index.svelte

src/routes/dev/variables/[variable]/inputs/[date].svelte

src/routes/dev/variables/[variable]/parameters/[date].svelte

src/routes/dev/variables/index.svelte

src/routes/index.svelte