View assets detail and download operation (#198)

* Fixed not displaying default user profile picture

* Added buttons to close viewer and micro-interaction for navigating assets left, right

* Add additional buttons to the control bar

* Display EXIF info

* Added map to detail info

* Handle user input keyboard

* Fixed incorrect file name when downloading multiple files

* Implemented download panel

web/src/lib/components/asset-viewer/intersection-observer.svelte

@@ -0,0 +1,55 @@
+<script lang="ts">
+	import { onMount } from 'svelte';
+
+	export let once = false;
+	export let top = 0;
+	export let bottom = 0;
+	export let left = 0;
+	export let right = 0;
+
+	let intersecting = false;
+	let container: any;
+
+	onMount(() => {
+		if (typeof IntersectionObserver !== 'undefined') {
+			const rootMargin = `${bottom}px ${left}px ${top}px ${right}px`;
+
+			const observer = new IntersectionObserver(
+				(entries) => {
+					intersecting = entries[0].isIntersecting;
+					if (intersecting && once) {
+						observer.unobserve(container);
+					}
+				},
+				{
+					rootMargin,
+				},
+			);
+
+			observer.observe(container);
+			return () => observer.unobserve(container);
+		}
+
+		// The following is a fallback for older browsers
+		function handler() {
+			const bcr = container.getBoundingClientRect();
+
+			intersecting =
+				bcr.bottom + bottom > 0 &&
+				bcr.right + right > 0 &&
+				bcr.top - top < window.innerHeight &&
+				bcr.left - left < window.innerWidth;
+
+			if (intersecting && once) {
+				window.removeEventListener('scroll', handler);
+			}
+		}
+
+		window.addEventListener('scroll', handler);
+		return () => window.removeEventListener('scroll', handler);
+	});
+</script>
+
+<div bind:this={container}>
+	<slot {intersecting} />
+</div>