groups: prevent accidental group deletion

Fixes https://github.com/urbit/landscape/issues/68

pkg/interface/src/logic/lib/util.js

@@ -327,11 +327,18 @@ export function numToUd(num) {
   )(num.toString())
 }
 
-export function usePreventWindowUnload(shouldPreventDefault) {
+export function usePreventWindowUnload(shouldPreventDefault, message = "You have unsaved changes. Are you sure you want to exit?") {
   React.useEffect(() => {
     if (!shouldPreventDefault) return;
-    const handleBeforeUnload = event => event.preventDefault();
+    const handleBeforeUnload = event => {
+      event.preventDefault();
+      return message;
+    }
     window.addEventListener("beforeunload", handleBeforeUnload);
-    return () => window.removeEventListener("beforeunload", handleBeforeUnload);
+    window.onbeforeunload = handleBeforeUnload;
+    return () => {
+      window.removeEventListener("beforeunload", handleBeforeUnload);
+      window.onbeforeunload = undefined;
+    }
   }, [shouldPreventDefault]);
 }

pkg/interface/src/views/apps/publish/components/MarkdownEditor.tsx

@@ -30,7 +30,7 @@ const PromptIfDirty = () => {
   return (
     <Prompt
       when={formik.dirty}
-      message="Are you sure you want to leave? You have with unsaved changes."
+      message="Are you sure you want to leave? You have unsaved changes."
     />
   );
 };

pkg/interface/src/views/landscape/components/GroupSettings.tsx

@@ -83,8 +83,11 @@ export function GroupSettings(props: GroupSettingsProps) {
   };
 
   const onDelete = async () => {
+    const name = association['group-path'].split('/').pop();
+    if (prompt(`To confirm deleting this group, type ${name}`) === name) {
       await props.api.contacts.delete(association["group-path"]);
       history.push("/");
+    }
   };
 
   const disabled =