Error when a user has no workspaces

[davidknight-seequent]

When a user signs-in with one of the Jupyter notebooks and selects their organisation and their Evo instance, if they haven't been assigned to any Evo workspaces yet they will see an error like the one below:

Perhaps this issue should be split into two issues, but it would be great if we could solve two things:

1. If a user doesn't have access to any workspaces, handle this situation gracefully and show a nice message instead of a giant Python error.
2. For all users, whether they have access to workspaces or not, show an addition option "Create a workspace" that allows them to simply enter a name and then click a button to create a workspace. We should also provide a brief sentence explaining that they can visit the Evo portal for further customisation.