fix: Add alt attribute to all image nodes

Signed-off-by: Julius Härtl <jus@bitgrid.net>

src/nodes/ImageView.vue

@@ -62,6 +62,7 @@
 						<div v-else contenteditable="false">
 							<img v-show="loaded"
 								:src="imageUrl"
+								:alt="alt"
 								class="image__main"
 								@click="handleImageClick"
 								@load="onLoaded">