Further delay animation creation in Behavior.

Further delay animation creation in Behavior.

Previously we always created the animation on the first call to write,
regardless of whether the Behavior was enabled. Now we delay until the
animation is needed.

Change-Id: I14a319a4f045050fe6a99427b7c3804ef078d48d
Reviewed-on: http://codereview.qt-project.org/5414
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Charles Yin <charles.yin@nokia.com>