remove concept of 'week' from public curriculum in favor of units

As we began assembling the daily lesson plan for the first 3 months, @bookis and I both realized that the order of the weeks was different than what we wanted to do, and that the schedule as proposed by the curriculum repo was itself inconsistent about which weeks were which. Not every "chunk" of lessons fit neatly within a week, and we instead preferred to think of the "weeks" not as units of time, but units of knowledge. This change scrubs the repo of the idea that the "lesson units" are weeks. 

(It feels a little like rearranging deck chairs, but its helpful to our conversations about what happens when.