We are working on getting better sprite support into the app.
In the meantime, here are two ways that might work
1) In animator create an square object and set the overflow to hidden. Inside this object add an image object (your sprite sheet). Then you can animate the inner object and add two keyframes for each sprite. E.g. keyframe 1 at 0s shows sprite 1, keyframe 2 at 0.10s shows sprite 1, keyframe 3 at 0.101s shows sprite 2... etc...
2) Include some custom js, in the start action that will change the image position
get sprite sheet
move sprite sheet so next sprite is shown