Namespace license checks for audit events

Related to https://gitlab.com/gitlab-org/gitlab-ee/issues/2335

Audit events (EES / Bronze)

1. Do not show Audit Events under Project -> Settings

2. Do not show Audit Events under Group -> Settings

3. Show 404 for /<groupname>/<projectname>/audit_events & /groups/<groupname>/audit_events

Expert: @jameslopez

mentioned in issue #2335 (closed)

assigned to @to1ne

mentioned in merge request !2326 (merged)

closed via merge request !2326 (merged)

mentioned in commit 2f6b1b58