revisions to the open science lesson plan

Revisions follow along the lines of the proposal discussed in https://github.com/swcarpentry/bc/issues/712

Given the potentially more subjective nature of this particular lesson, I found some of the revisions challenging to implement.  I have tried to focus the lesson on providing students with the information they would need if they chose to make data or software openly available, rather than trying to convince them of what they _should_ do. Please let me know if this leaves any part inadequately motivated, or if there is anywhere I have been too prescriptive on a subjective topic. 

Even while though I've avoided the cultural/philosophical discussion, the lesson is still not particularly hands-on.  I'm curious if people feel that students would be better served by a tutorial in which they actually deposit data or share code on a particular repository, license and all.  The downside of that approach is to disproportionately emphasize one particular repository over the others (which is why I avoid a specific example). 

I have tried to keep the lesson to the length of the former, but not having taught that before I'm not sure how long it takes.  I imagine this is one lesson instructors might use rather flexibly, skimming through the essentials very quickly if running behind schedule.  I've tried to be concise and rely on external links for elaboration, but nevertheless some parts could be tightened up. 

I've marked a few points with inline HTML comments where specific feedback would be helpful.