Removed unused import
Check for permissions by using the decorator
Removed extra closing div tag
New semantics for the `view` permission

The `view` permission is now project-centric, therefore it can only be set
at the root directory and at the top-level of projects.

The wording has changed, and previous permissions are cleared at upgrade
time.

Part of #3.
Moved Project/Language cached object retrieval to managers

Ideally the logic should be implemented as a inheritable manager so
arbitrary models can make use of object caching mechanisms for any
querysets.

In any case, this helps to reuse the code in other places where the cached
objects could be of some use.