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.
Changes for Help Modal to work on Stanford Site

- moved zendesk endpoint to new condition
- some help modal styling
lti 2.0 result service rest endpoint

Conflicts:
	lms/djangoapps/courseware/tests/test_module_render.py