Fix tablev1 spec

[JCZuurmond]

Thought that #190 introduces the TableV1Spec, the integration test show the tables, however upon further inspection, the table is automatically converted to a new table

Not a problem on itself, though we would like to avoid the warning. However, it became a problem when introducing columns that https link to resources. Then we get an error that the widget definition is invalid.

For testing, I trimmed it down to:

• ✅ Update the integration test dashboard.json to include a table based on old TableV1Spec. (No column links, but it has the option to do so.)
• ✅ Import manually to see if the json contains a valid dashboard
• 🚫 Deploy the json via an integration test -> this results in an invalid widget:

[JCZuurmond]

Solved by always adding the invisibleColumns to the body