Keep unknown datatypes when importing

[psychowood]

Describe the bug
Not sure if this is a bug or rather a feature request, but since many datatypes exists that are not directy supported in the importar, it could be useful to import the type as is in the sql file instead of clearing that information.

To Reproduce
Steps to reproduce the behavior:

1. Import a column in a not supported datatype (es. numrange in PostgreSQL)
2. See that the datatype is empty in the resulting table

Expected behavior
Keep that type. If the json is edited manually, the datatype can be set and shown in the diagram.

Additional context
Perhaps making the datatype field editable besides having some autocomplete suggestions could avoid the issue.