Add headers.

RESTful responses have to use correct headers, depending on the request.
Add Fail test-cases
Reflect altered page-layout
Add Tests for Articles Subcontroller
Add Articles-Subcontroller
Merge branch 'skeleton' into feature/admin_tool
Merge branch 'tests/admin_tool' into feature/admin_tool
Add model for topics
Add model for articles
Merge branch 'feature/admin_tool' into tests/admin_tool