Houdini: any outdated containers and validate fps popup don't work

[BigRoy]

Describe the bug

The "Scene has outdated content" pop-up and FPS validation pop-up for Houdini scenes does not work.

In particular due to:

• this setButtonText method not existing on the Popup class
• this on_clicked signal not existing, instead its called on_show

Not sure where this bug got introduced.

To Reproduce
Steps to reproduce the behavior:

1. Go to Houdini
2. Set invalid FPS for current scene.
3. Save and reopen file. See error message.

or

1. Go to Houdini
2. Load old version of a model
3. Save and reopen file. See error message.

[cuID:284bh08]