(Added) update label option for source.

tui_rsync/models/models.py

@@ -82,6 +82,10 @@ class Source(BaseModel):
         src.save()
         return src
 
+    def update_label(self, new_label):
+        self.label = new_label
+        self.save()
+
     def update_args(self, args):
         args_obj = SyncCommand.get_sync_command(args)
         self.args = args_obj