Remove student statistics.

[somiaj]

The student statistics and student progress page are identical. Remove the student statistics version of the page, since the page doesn't provide any summary of the data, and only shows a student's number of attempts and grade.

[drgrice1]

I haven't looked over the code thoroughly yet, but I can already see how much this cleans up the mess of trying to share the templates between the stats and progress pages that I had to go through when I converted to using Mojolicious templates. I will try to look the code over better later, but I am sure it is generally good.

[somiaj]

@drgrice1 I noticed that the siblings template was also shared. This one was a little harder for me to decide if it should be split into two places or not. There are differences between then (stats will never need to create a student list, while student progress never creates problem list), but there is also a lot of overlap too. I split them just to try to limit sharing (there really isn't a centralized place to share templates), it also keeps from having to find/replace the current_route string each time. I made it a second commit just to make it easy to revert if we still want to share this template between the two modules.

[somiaj]

I went with only sharing the code that links to the sets, but the unshared code is in individual templates.