feature preview framework
Merge branches 'settings-redo' and 'feature-preview' into scratch

Conflicts:
	corehq/apps/domain/urls.py
	submodules/toggle
Add smarter handling of ES errors
modifies fixture-filters to use fixture-with-attributes
modifies fixture-filters to use fixture-with-attributes
modifies fixture-filters to use fixture-with-attributes
basic fixture model migration
modifies a fixture couch-view for attribute support
renaming fields method
move Address generation to helper function
use email rendering for bookkeeper table
add contact info to bookkeeper email
modifies report-filters-using-fixtures to attribute-fixture-filters
modifies custom-apps-filters to be compatible with fixtures-attributes
modifies Fixtures upload for attributes
casting ints from excel to strings to store in couchdocs
better exception handling
fixture api better upload exception
fixtures style changes from review
adds fixture-download with attributes