We will take this opportynity to remove various QStyle specializations
from the public API in Qt5. This gives us much more freedom, for
example changing the inheritance hierarchy, pluginizing etc. without
worrying about BC.
=> Use QStyleFactory and/or QProxyStyle instead of creating an instance
or inheriting QMacStyle directly.
Change-Id: I44a2f5ee3fe08ecc837b593a2a2737eb90e8c267
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>