Verified part and question ordering is working correctly on nightly 13

Yeah, I know. My PR (hopefully) accomplishes that*. But I thought Tiffany (or whoever) might like to know how it was actually behaving until now, because it will still be like that on 11.x versions.

*Incrementing consecutive parts instead of swapping. Modified positions will be prioritized, the rest will fill the gaps considering their previous position. Added warning for users choosing repeated destination positions.

Hi Bernardo,

It's been my experience that the original description of the issue applies also to questions and not just to parts, as Derek mentioned above.  Within a single part, if you try to reorder questions, it switches questions. i.e. Set up a test with 5 questions in a single part.  If you want to move question 5 to the top space - you change the question number to 1 and click update order. It then switches questions 1 and questions 5.  The expected behavior would be that it would make question 5 into the new question 1, question 1 into the new question 2, and so on until question 4 becomes the new question 5.  

We're going to change the behaviour of the reordering, so the bug won't be present. Also, I think we shouldn't allow instructors to select the same position for different sections/questions, so we might add an alert to avoid it. Guess we can use this JIRA for all that.

For now, you might also want to know that (I believe) the bug does not appear when ordering questions, only with sections.

Ah, ok, thanks!

Regarding the bug, I guess the question then is for a developer - is the bug I experienced different or the same as the one @Sam Lee Pan reported here?  If it's different, I'll create a new jira.  Or maybe there needs to be a parent issue of "part reordering bugs" with two subtasks?