Sprites can now have varying width and height

Sprites can now have varying width and height

Varying between Sprites, or between width and height, not within a
single Sprite. For ImageParticle only, SpriteImage changes will be in a
later commit.

Also adds spriteInterpolation boolean.

Change-Id: I80681e44f26985a6f6a6b83bd162f6231c7f28c4
Reviewed-on: http://codereview.qt-project.org/6002
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Martin Jones <martin.jones@nokia.com>