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

Conflicts:
	corehq/apps/domain/urls.py
	submodules/toggle
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
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
download fixtures with excel
minor fixes in fixture-download
adds another excel-check for fixture-upload
output empty string instead of None in fixture-xml