Bug 854417 - Smarter redraw of SMS list

This is my experiment that I have been working on a bit. It brings initial rendering time of a list of 1,000 items down by a factor two. Subsequent redraws are infinite faster because it redraws based on a hash.

It doesn't lint at the moment, but I want some feedback first before continueing. @borjasalguero @rwldrn @fcampo