replace folders with categories (WIP)
resolve some todos
fix issue
protect files

Files are only accessible over the download controller to ensure that
the user has the needed permissions.
fix last commit
finalize replacing folders with categories
fix last commit
Merge branch 'master' into fileSystemOverhaul
drop support for files without category
Specify category when uploading a file
Merge branch 'master' into fileSystemOverhaul
fix page title
Fetch file details on demand
clipboard actions for files
fix issues regarding file upload
make file list sortable
fix issues
assign file to more then one category
remove information tooltip
improve upload