Replace vue-multiselect with a custom component (#366)

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/frontend/pulls/366
Co-authored-by: konrad <konrad@kola-entertainments.de>
Co-committed-by: konrad <konrad@kola-entertainments.de>

src/helpers/closeWhenClickedOutside.js

@@ -0,0 +1,27 @@
+/**
+ * Calls the close callback when a click happened outside of the rootElement.
+ *
+ * @param event The "click" event object.
+ * @param rootElement
+ * @param closeCallback A closure function to call when the click event happened outside of the rootElement.
+ */
+export const closeWhenClickedOutside = (event, rootElement, closeCallback) => {
+	// We walk up the tree to see if any parent of the clicked element is the root element.
+	// If it is not, we call the close callback. We're doing all this hassle to only call the
+	// closing callback when a click happens outside of the rootElement.
+	let parent = event.target.parentElement
+	while (parent !== rootElement) {
+		if (parent.parentElement === null) {
+			parent = null
+			break
+		}
+
+		parent = parent.parentElement
+	}
+
+	if (parent === rootElement) {
+		return
+	}
+
+	closeCallback()
+}