adding debug toolbar and config, allowing local_settings to specify INSTALLED_APPS and MIDDLEWARE_CLASSES
make users define USE_DEBUG_TOOLBAR, to use the debug toolbar.  Disabling context output, as it can be too heavy for our app. Changing querystring key to "debug"
using database sessions cache in DEBUG mode is NICE
Merge branch 'release-0.10' of github.com:learningequality/ka-lite into debug_toolbar

Conflicts:
	kalite/coachreports/api_views.py
tweaked ordering of local_settings/settings, always use db-backed mem cache for sessions, simplified decorator for profiling API calls.
Merge pull request #494 from bcipolli/debug_toolbar

Add Django debug_toolbar (when USE_DEBUG_TOOLBAR=True); allow INSTALLED_APPS (& more) in local_settings