Improve error message on missing lib/scripts (Fix #9785)

Now when lib/scripts is deleted or removed, a more appropriate
error message is thrown. The server, however, won't start up
in this condition, and any attempt to read the directory results
in an `InternalException`.
Added metadata call to load the parents of FileAnnotations
Renamed 'Unlink' option to 'Remove'
Overhauled 'unlink' and 'delete' attachment options

Removed 'delete' option (attachments cannot explictely deleted anymore,
instead are deleted automatically when the last link is removed)
Renamed 'unlink' option to 'remove'
Added a proper warning dialog instead of using a Messagebox
Added some comments
Switched to HashMultimap
Fixed weird indents
Fixed wrong import
Fixed various minor things
Removed unneccessary code
Truncate long file names
Fixed "Remove ... by me / by others" bug
Just cleaned up the messy import statements of the previous commit again
Fixed indent
Close ImportProcessPrx instances (Fix #12233)

Once upload is completed, the import process instance should
be closed. The `HandlePrx` which is returned will continue
functioning.
Fixed minor typos in webadmin views
Disk usage by group or user loaded by json
Table and progressbar updating with json data
Show disk usage by single user/group