Fix STUD-1316

This bug affected unpublishing content (and would trigger an error
message in studio). The fix was to uncouple the rendering of the studio_view
of an xblock with the student_view, so that content that wasn't in
draft mode already wouldn't be modified by early rendering of the
studio_view.

[STUD-1316]
Merge pull request #2628 from cpennington/fix-stud-1316

Fix STUD-1316
Rollback Django Debug Toolbar from 1.0.1 to 0.9.4

Due to issues with require.js and the latest version of the toolbar.
Also included a note in the requirements file explaining the situation, and what
needs to happen before this can be upgrade properly.

Conflicts:
	lms/envs/dev.py
Merge pull request #2650 from edx/zoldak/dbt-onto-release

Rollback Django Debug Toolbar from 1.0.1 to 0.9.4
Merge branch 'release'