webadmin: Double click collapse system tree

- Added quick way to collapse the system tree with a double click
- Added ability for the client to remember the system tree width
  state.
- Added a collapse button to quickly collapse the tree.
- Added an expand button to expand the tree if it is hidden.

Change-Id: Ida98ac456d9dd325ba1bf5676671bf53b5c3173e
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=999713
Signed-off-by: Alexander Wels <awels@redhat.com>