Fix targeted-feedback bug

The bug is with the case of multiple-questions with targeted
feedback within a single problem.

Refactor the targeted-feedback tests to house
the most common xml in external files.

Move the capa test load_fixture function to __init__.py so it
can be used generally.
Modify paver run_all_servers to allow different settings for LMS and Studio.
Added username as option for batch enrollment/unenroll
Additional logic to handle more course_image URL edge cases
This changes logic to allow more missed use cases of course_image to
work properly.  The cases are:

. XML courses with the course_image attribute set
. Mongo courses that are imported without a contentstore
. Mongo courses that have course_image set but don't have a content store

It also exports default images_static_course.jpg to
images/static_course.jpg to handle a use case where a course author
uploaded an image to the default location in studio without using the
studio interface for adding course images, they then export the course, and then
import it without a contentstore
Corrected test names and doc strings
Simple fixes

- Ensure temp files are cleaned up.
- Refactor a function with three return statements.
Add my name to the authors file
Fix #3347: "Run Code" reloads page in Matlab Problem

Instead of refreshing only the necessary parts,
"Run Code" reloads the whole page.

This commit fixes this behaviour, by refreshing the
specific elements belonging to the Problem instead.

Also tidies up indentation.
CMS: debug toolbar should be displayed on dev stack.

In Studio, the debug tool bar did not appear as in LMS.
Add myself to AUTHORS.
Update translations (autogenerated message)
Allow creation of components on container page

This commit implements STUD-1490, allowing creation of components
on the container page. It also enables the delete and duplicate
buttons now that new content can be created that would benefit.