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