Fix: insert backend modules in the backend sub-package namespace on import.
Fix: insert backend modules in the backend sub-package namespace on import.

chrisidefix/visvis,Alwnikrotikz/visvis,chrisidefix/visvis,Alwnikrotikz/visvis,chrisidefix/visvis,pbfy0/visvis,Alwnikrotikz/visvis,pbfy0/visvis,pbfy0/visvis.dev,chiluf/visvis.dev,Alwnikrotikz/visvis.dev,pbfy0/visvis,AlanZatarain/visvis.dev,almarklein/visvis.dev