notes: add icons to use previous/next event as template

app/src/main/java/it/danieleverducci/lunatracker/MainActivity.kt

@@ -334,7 +334,7 @@ class MainActivity : AppCompatActivity() {
                     updateContent(prevEvent)
                 }
             } else {
-                nextTextView.visibility = View.GONE
+                prevTextView.visibility = View.GONE
             }
         }