Merge branch 'fix/licence' into 'master'

Clarify licencing situation

Closes #505

See merge request !568

LICENSE.md

-### GNU AFFERO GENERAL PUBLIC LICENSE
+# Thalia Code
+
+The code by members of Thalia's Technicie is available under AGPL included below.
+
+# Theme
+
+The style files and theme may only be used by Thalia and is under licence from ThemeForest.
+
+# GNU AFFERO GENERAL PUBLIC LICENSE
 
 Version 3, 19 November 2007