webadmin: bookmarks first try

- Bookmarks are not working the very first time you try, if
  you hadn't selected anything in the system tree yet. This
  was due to a system tree reset in bookmarkListModel_Navigated.
  This patch removes the reset and moves it into event handler
  that shows the system tree when moving from bookmarks or tags.

Change-Id: I323869918c0affe15281526983e936db18ad6506
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1110444
Signed-off-by: Alexander Wels <awels@redhat.com>