Access a directory through file manager when not all parent directories are visible for the logged in user

[Nicklas Nordborg]

See #982 for background.

The file manager loads the directory tree top-down, starting at the root directory or the home directory of the logged in user. Directories that are not readable by the current user are not included. This means that sub-directories to non-readable directories can't be included either even if the logged in user has permission to access them. This is usually no big deal but may affect project cooperation when analyzing data with plug-ins that create directories inside a project directory. This directory is usually linked from the transformation page. But if the complete parent path is not readable by the user, the project directory is not accessible from the file manager and the user ends up in the home directory instead of in the project directory.

The workaround is to make sure that the logged in user has at least READ permission to all directories in a path up to the root directory.

Possible solutions

1. When the display of a specific directory is requested that is not reachable from the root, the file manager should create a top-level entry that shows the requested directory and it's subdirectories.

2. Extend the default file tree with a new top-level entry containing experiments that has a project directory. One potential issue with this solution is that we must be able to handle that the same directory is appearing in multiple places.

+Experiments
  +Exp A
    subdir1
    subdir2
  +Exp B

3. Both 1 and 2.

[Martin Svensson]

(In [4742]) References #1178 First alternative is in place but the second alternative needs some more work.

[Martin Svensson]

(In [4744]) Fixes #1178 Access a directory through file manager when not all parent directories are visible for the logged in user. The second alternativ, with experiment directories, will be abandon. The time to load the tree will be too long for those users with permission to view many experiments.