Apache WebDAV doesn't respect ACLs

[meredithdutton]

Apache WebDAV doesn't respect ACLs of authenticated user, so these are implemented as Apache config files on a per-user basis, requiring an apache restart whenever a user is added or removed.

The current functionality could be implemented by wrapping PyWebDAV. It would also remove a dependency on Apache for anyone who wants to deploy the DataStage web interface in another environment.

[meredithdutton]

By implementing access control based on the actual ACLs on files and directories, we can be more certain that people won't be able to access stuff they shouldn't through the web interface.

As an example, a user might believe that by changing the permissions on a file in the shared or collab areas that those permissions would be respected. However, the WebDAV interface would continue to allow access as before.