Drop Python Intro

[kelle]

Consider dropping Python Intro and rearranging schedule accordingly.

Instead, send folks pre-req materials to be sure they have some Python Intro ahead of time. (I'll make a new issue for that.)

[eteq]

@pllim, @stargaser and I discussed this and we agreed that's a good idea when coupled with #60. I'll do a tentative re-work of the schedule on that basis (i.e. step 1 of #65)