Added new Page Not Found component, updated route to use new component

[arunapa]

Completed Note: PR to be updated with code to explicitly redirect users to 404 page when they request a resource that cannot be found

• tested by providing an incorrect file url, verified redirects to page not found

[longshuicy]

hm actually i can't trigger this 404. whenever I gave a wrong URL, i get 500 error. E.g.

role = AuthorizationDB.from_mongo(authorization).role
AttributeError: 'NoneType' object has no attribute 'role'

[longshuicy]

To test:

1. go to a non-exist routes for example /datasets or /files or /something random
2. edit file id in the URL but you have to match digits to make it a valid objectID