DataModel removed in ss4-beta4

[Jack O'Connor]

DataModel has been removed in ss4-beta4 and so is causing breaks in GridFieldBetterButonsItemRequest.php on lines 75 & 89.

[Tim]

also, the class SilverStripe\ORM\Versioning\Versioned has moved to SilverStripe\Versioned\Versioned

[mr-macedawg]

#170
Hopefully @unclecheese approves this. I have manually made these changes on my site to confirm it works.

[Martimiz]

Hi uncle, all

Namespace also needs fixing in BetterButtonDataObject, just noticed...

Has anyone got this working for versioned dataobjects yet? Even with these fixes, for me the cms (4 stable) just hangs on loading (page reload)...

[Elliot Sawyer]

I have raised a PR for this here: #172

I have closed my PR, somebody else has raised one here: #170