Implement better coupling of reset/undo function/a nearer undo button

[rugk]

See rugk/offline-qr-code#309

• I very much like the idea of the undo button getting switched and having undo functionality. However, it would not match the current style, be a rather big implementation thing and the success notice itself is also important if you don't want to undo it. If you don't see that, that is bad, anyway.
• Moving the green result message nearer to the button is IMHO a simple, straightforward to implement and clever (enough) solution (for now). It also solves the problem of not getting any (good) response to your user action.
  Note: may be my personal preference, but the message should still be at the top of the reset button.

Implementation

Should be as simple as getting/changing the ID of the MessageBox to use a custom one that is placed at the correct position.

https://github.com/TinyWebEx/PermissionRequest does something similar/is used in the same way.