Fix accessibility of PSMTabBarControl
Fix accessibility of PSMTabBarControl

* it's now an AXTabGroup - thanks to AXTabs the position of the tab
  and total tab count are announced
* AXChildren shows only visible tabs, and all buttons (like overflow)
* AXValue + AXValueChanged notification enable announcing new tab name
  when switching between them with Cmd-Shift-[] (for unknown reason
  this does not work quite yet)

neoneye/PSMTabBarControl