Suggest lossless save (metadata save) when only metadata-related actions are used

- when the "run action" button is pressed and no "save" action is present,
- check if the action(s) selected involve only metadata manipulation.
- if that's the case, the "save tags" action should be added (not the general "save" action), or you should get a warning about that possibility.

You should also get a warning if you deliberately choose the standard "save" action when lossless save (currently "save metadata") is possible.