code review

Hi @pmitros @singingwolfboy ,

This is a module we previously built to allow students to recommend useful resources for problems and share resources with their fellows. We have tested it in two runs of 6.00.1x. We are now attempting to make it into production. I was wondering could you help us do the code review. It was checked as an R&D prototype (https://github.com/pmitros/RecommenderXBlock/commit/b4f3596d095d88bb4540f0d04ab81836d84edc98)
, and we made several changes to it (https://github.com/pmitros/RecommenderXBlock/commit/b41ba8778b98da0ea680ffb8bbc59492d669df2d).
Sorry but I still can't find how to compare two repositories which are outside edx-platform; thus, I just lists them here, and I was wondering how to do that.

Besides, there are testcases for this module: https://github.com/edx/edx-platform/pull/4845