[Fix] Flexible router.
[Fix] Add path prefix middleware.
[Update] Add pathprefix middleware in express.
[Update] Furnish the model with reference.
[Update] Update the routes.
 - The article's url now is not related to catalog.
 - To find the catalog's articles, the catalog's id should be set in option 'catalog.id' instead of 'catalog'.
[Update] Update the view to reflect the changes.
Merge branch 'master' of github.com:yfwz100/neuola