Convert schedule to Liquid template

This branch converts the schedule back from static HTML to post-driven, relying on the original session posts.

I intentionally made zero changes to CSS in order to make QA super-simple. It actually made me learn a couple really neat features of Jekyll to produce the exact markup we already had.

I did a check and during my testing the branch was absolutely pixel-perfect identical to the live site. I feel good about this one :yellow_heart: