Replace 'create collection' with a CbrainTask

[natacha-beck]

We need a new CbrainTask that allows a user to repackage
any part of a set of userfiles (or file collections)
into a new file collection, with options to choose
the target file structure. For instance:

• Start with several CivetCollection; specify
  the files "surfaces/grey_surface.obj" and
  have them all packaged into a new flat
  FileCollection
• Again with several CivetCollection, select the
  same files but this time have them put into a separate
  directory named for each original CivetCollection,
  inside the new FileCollection.
• Other renaming rules for individual files or folder.
• Allow the task the preview what will be done by showing
  the file list of the source userfiles and highlighting
  in red the entries that will be selected for copying.
  Show the resulting output file too. Use the
  'Refresh' mechanism of the PortalTask API to make this
  interactive.

On BrainStorm, I'd configure this task to run on InstantUnix,
so that once triggered the full execution cycle goes through
almost immediately.

Related: 1682, 2086 || #39