ui: add reltime rendering

Signed-off-by: William Casarin <jb55@jb55.com>

src/notecache.rs

@@ -14,4 +14,8 @@ impl NoteCache {
         );
         NoteCache { reltime }
     }
+
+    pub fn reltime_str(&mut self) -> &str {
+        return &self.reltime.get();
+    }
 }