implement HTTP POST method

Webserver/src/routes/image/+page.svelte

@@ -16,6 +16,20 @@
 		await post(fdata, 'upload');
 	}
 
+	async function post(fdata: FormData, endpoint: string) {
+		// Append endpoint to formdata for redirection
+		fdata.append('endpoint', endpoint);
+		// Send request to be redirected to given endpoint
+		const response = await fetch('/api/redirect', {
+			method: 'POST',
+			body: fdata
+		});
+		// Await respose from webserver
+		const mdata = (await response.json()) as APIResponse;
+		// Basic error handling
+		if (!mdata.success) alert(`Error while processing '${endpoint}'!`);
+	}
+
 	async function fileAsDataURL(file: File, width: number, height: number): Promise<string> {
 		return new Promise((resolve, reject) => {
 			const img = new Image();