webadmin: Update tree title to System

- Updated the main tree title to say System instead of Tree

Change-Id: I24c7f4aec1031e6f4c20a3c71de474f01d0b5ee7
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=879308
Signed-off-by: Alexander Wels <awels@redhat.com>