While the folder picker had some shared code with the file picker,
the folder hierarchy made some sense, but since it's gone now,
move the files to the base directory.

Change-Id: Ib78ada9cdb570df64ccbc28da835cfcaf25009db
Reviewed-on: https://gerrit.libreoffice.org/60145
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>