Fixed compile of examples and tests.

6aad4122332c0291e2e3249b508c7583428177b9 in qtbase removed implicit
linking to libQtWidgets.  Projects which implicitly used that module
were broken.

Either remove the dependency where it is not required, or explicitly
opt-in to libQtWidgets where it is required.

Change-Id: I6f4fb1d98bdf5bb65b4f02a1d245d334314b163d
Reviewed-on: http://codereview.qt-project.org/5268


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Toby Tomkins <toby.tomkins@nokia.com>
Reviewed-by: Alan Alpert <alan.alpert@nokia.com>