Work around wrong click area of output buttons on Mac.

For some reason using push buttons in the status bar will make
the clickable area of the buttons too small (half of the button isn't
clickable). Using QToolButtons instead.

Task-number: QTCREATORBUG-4513
Change-Id: I8b0f97552ec9b2471d570d577522b7ce5f382fb9
Reviewed-on: http://codereview.qt.nokia.com/2193


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Leandro T. C. Melo <leandro.melo@nokia.com>
Reviewed-by: Daniel Molkentin <daniel.molkentin@nokia.com>