Add initlal service-worker with basic offline handling. Manifest is not yet present.

src/routes/+error.svelte

@@ -29,7 +29,7 @@
 		</div>
 	{/if}
 
-	{#if $page.error?.owlCode === 'NETWORK_DISCONNECTED'}
+	{#if page.error?.owlCode === 'NETWORK_DISCONNECTED'}
 		<Button onclick={() => window.location.reload()} color={'accent'}>Retry</Button>
 	{:else}
 		<Button href={'/'} color={'accent'}>Return to Home</Button>