IDEA-83595 Allow adding more than one gradle project

1. Don't modify project-level settings (e.g. language level) on importing a module from external system;
2. Ensure that ProjectDataService implementations preserve 'importData()' contract (don't re-create an existing project entity);
IDEA-83595 Allow adding more than one gradle project

Don't reuse ExternalProjectSettings object from 'import from external system' wizard at the external system settings (the wizard used to modify data of the project imported previously during the same ide session)