Add SwaggerUI to 3.18.3 to handle OAS 3.0 specs and keep using current swagger for older specs.
See compatibility matrix of SwaggerUI
1. Add swagger UI JS version 3.18.3+ to handle OAS 3.0 specs. Put the new version in cdn/swagger-ui directory.
2. Make some tests: create a Swagger spec 1.0 and 2.0
3. Add another liquid drop to handle displaying OAS 3.0 spec in developer portal (pair with ruby side if needed)
4. Test in the developer portal and admin portal to see where it breaks, fix them
use `active_docs` liquid tag to include the correct swaggerui lib or just base it on info we have in db on swagger version that needs to be rendered
QE note: This should be tested with this issue https://issues.redhat.com/browse/THREESCALE-4356