HTC's One M8 is among the best-designed phones we've ever seen. It works well, it's powerful, and it's beautiful. Now, in an effort to find a way to make its best phone a little cheaper, HTC is releasing the One E8, a phone with all the trappings of the M8 except for a plastic body and a much lower price tag. The question for HTC: can it change its best phone without changing what makes it special?