userportal, webadmin: ScrollableTabBar

- Added new ScrollableTabBar widget to replace the flow panel in the
  main tabs and sub tabs. The widget is a GWTP PresenterWidget.
  - The bar has the following properties:
  - A left/right scroll button appears when there is not enough room
    to show the entire tab bar.
  - A 'drop down' button appears that when clicked displays a list of
    all the tabs.
- For the sub tabs I am using the view as a regular widget. As the
  SimpleTabPanel is not GWTP aware.
- Updated AbstractActionPanel to be cascade aware.
- Updated user portal to use scrollable tab bar in extended view.
- Updated user portal to use cascading action panel for buttons.

Change-Id: I63dddb3c0026ea3a5c13c3d18daebd02e13b1043
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=818051
Signed-off-by: Alexander Wels <awels@redhat.com>