userportal,webadmin: clear subtab item

- When unselecting a main tab grid item, the active detail
  model was not cleared. This caused the detail model to not be
  refreshed when re-selecting the item in the main grid.
  This patch clears the active detail model when unselecting
  the item in the main tab grid.

Change-Id: I5309207cb8153f7b1d5c8e53a117dd8440a98698
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1131147
Signed-off-by: Alexander Wels <awels@redhat.com>