#23 do not use copy for NSURL properties and add a node object for the
 outline view
#23 cache nodes for outline view
#23 use node in double click handling
Merge branch 'master' into issue/filebrowser-bug-23
#23 small refactoring
Merge branch 'master' into issue/filebrowser-bug-23
#23 reformat
#23 add test for file browser outline view datasource
close #23: Merge branch 'issue/filebrowser-bug-23'