[DS] Specify tight core, with optional exercises for stats, CS, etc

[schanzer]

Based on @shriram 's email:

On Aug 9, 2018, at 10:

31 PM, Shriram Krishnamurthi sk@cs.brown.edu wrote:

That' fair. But in the process we may also be boxing ourselves in. Also out of fairness to teachers, I think we need to be more explicit about what we're offering, and maybe it has to be advertised as (numbers are spitballs):

The module is designed to take 15 hours. There are optional materials that can be injected all through the module, taking it to 40 hours. In particular, a proper understanding of the power and perils of data science, which we believe is essential for the modern educated citizen, will require the incorporation of modules that take a total of 25 hours. But a course that can accomplish this through other means can skip these extra 10 hours.

I'm wondering if just laying out this way and appealing to their better natures will get them to automatically donate the extra time, because the first and immovable number they still see is 15; the rest is time they voluntarily provide to do the right thing.

[schanzer]

And from our evaluator:

[schanzer]

Tracked in Remix, on https://github.com/bootstrapworld/curriculum/issues/155