Update database schema (resolves #32)

Delete unsed "user" attribute in the Nxman entity and re-generate the PDF file.
Resolves #32.

There's not much to review hence this should be quickly closed, @Zboubidoo. Note that the issue will automatically be closed when the commit including `(resolves #issue-number)` suffix is merged into `v2` (which I just set as the default branch).