duplicated assignments default unpublished

https://trello.com/c/6eybL1SK/357-improve-duplicated-trainings-and-missions-should-be-unpublished
red background colour for unread post
enable user to see their own hidden posts
refactor: material_folder -> root_folder
material notification only show opened folder
better forum subscription UI
Merge branch 'development' of github.com:Coursemology/coursemology.org into Deploy
precompiled assets