Initial ImageParticle sharing

Initial ImageParticle sharing

This allows particles rendered by ImageParticle to share some of their
randomly generated state. Still to come are reset methods and animData
sharing (so animations can look synced)

Change-Id: Ia805e1b3735b15fba7bd14778ed7abd795b11f06
Reviewed-on: http://codereview.qt-project.org/5114
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Martin Jones <martin.jones@nokia.com>