[WIP] do not allow upload when no firewall is configured unless explicitly enabled

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | yes
| BC breaks?    | only edge cases
| Deprecations? | no
| Tests pass?   | see travis
| Fixed tickets | -
| License       | MIT
| Doc PR        | TODO

The current code did allow not authenticated users to edit content, if there is no symfony firewall configured in the security configuration. This fix limits this behaviour to when the user explicitly enables anonymous editing.