(WIP) Randomized selection from content libraries - Do not merge, for internal review

[bradenmacdonald]

This is a continuation of the prototype found in #1, extended to implement SOL-18 "As a content author, I am able to select a number of random content blocks that would be displayed in a LibraryContent block."

Testing instructions:

1. Check out this branch on a vanilla devstack (not solutions), and do paver install_python_prereqs and paver update_db
2. As 'edxapp' user, edit ~/cms.env.json and add "ENABLE_CONTENT_LIBRARIES": true to the FEATURES object.
3. Edit ~/cms.auth.json. Go to MODULESTORE > default > OPTIONS > stores - it should contain two or three entries. Re-order the entries so that the store with "NAME": "split", comes first in the stores list. (This makes split the default modulestore for any new courses.)
4. Start paver devstack studio and go to localhost:8001 in your browser.
5. Log in as staff, and create a new course.
6. Edit the new course in studio. Go to Content > Content Library. Click the link to create the library, then go back and refresh the page to see the new library.
7. Add some content to the library. (Graded problems not tested at this point - stick to content like HTML blocks rather than problems).
8. Go to Settings > Advanced Settings and add "library_content" to advanced_modules.
9. Go to Content > Outline. Create a new section and subsection, then edit it. Click "Advanced" and add a new "library_content" block.
10. Once the block is added, click "Edit" to edit its settings. Most are explained on the settings editor. For the "Library" setting, you must click "Add", then paste the CourseLocator of your library. This looks like course-v1:ProblemX+PR0B+2014+branch@library. (It's in the URL when you go to Content > Content Library, though the URL may not show the +branch@library part, so make sure to add that). Hit Save.
11. Click "Update now with latest components from the library".
12. Optional: Click "View >" to preview all the blocks found in the library.
13. Hit "Publish", then start up the LMS and go to localhost:8000. Browse into the course, and you should see that the block is replaced by random blocks from the library. To test the randomization, click the lowest "STAFF DEBUG INFO" link underneath the module, then click "Delete Student State", then refresh the page.

[Kelketek]

This checks out. I was able to get it running per the instructions and it works as advertised.

I did notice an oddity that isn't mentioned in the instructions-- When first visiting the Content Library link, I get a very basic unstyled response with a statement saying there is no content library, and giving me a link to create one. When I click the link, the result is JSON that loads in the browser. Is that expected?

The code itself doesn't raise any particular red flags for me. I'm good with this, if that previous note is expected and shall be resolved down the line as part of the project at large.

[bradenmacdonald]

@Kelketek Ah, right. I forgot to mention that in the instructions. Yes, that is the expected behaviour. It's unstyled and simple because this is just a proof of concept prototype. Once we have an approved design, and a UX plan, we will clean all those things up.

[antoviaque]

It's just a prototype so very minor at this point, but it could be worth moving the code selecting the blocks to its own method.

[bradenmacdonald]

Superseded by #5.