Add a use3dTransform option to disable 3d transforms at will.

Hi,

I find it useful to add a property directly to the transit plugin that allow you to enable / disable 3d transforms at will.
It's true that it's a boost to old ios (4-), but the fact is that using it on recents ios safari would cause text inside 3d transformed elements to be blurry.

I've added a commented line on the test file that allow you to quickly test on ios safari the feature.