Removal of tableau repository from Github

[Robbie GIll]

The repository for the tableau gem dependency has been removed from Github. Please see this commit on chorus master that removes the gem dependency and adds a stub to allow packaging and the existing test suite to complete successfully. 

Note: attempting to publish to tableau will fail. Future updates will be linked to this story.

Apologies for the lack of notice - Robbie

[Shell (Aridhia Informatics)]

Thanks Robbie, taking a look now.

S.