Menas doesn't handle Array of Arrays

## Describe the bug
If my data has a schema that includes an array of array, then the user is not able to properly work with them in the Menas. He can't assign default values or conformance rules on the second layer. And the schema is "improperly" shown in the schema tab.

## To Reproduce
1. Have a schema with an array of arrays. One schema added to the [Additional context](#Additional-context)

## Screenshots
The representation in schema tab

When chosen as a field for default value or a conformance rule

## Additional context
[Schema.txt](https://github.com/AbsaOSS/enceladus/files/3181712/Schema.txt) for testing purposes. In .txt format because GitHub doesn't support JSON.