add secure_submissions setting for apps

for CommCare 2.8+

Basic auth'd submissions feature is now ready to test end to end
Merge branch 'master' into app-secure-url
move secure submissions setting into Advanced (and remove Logging parenthetical)
Merge branch 'master' into app-secure-url
Merge branch 'master' into app-secure-url

Conflicts:
	corehq/apps/app_manager/static/app_manager/json/commcare-app-settings.yaml
	corehq/apps/app_manager/views.py
make secure_submissions app setting a preview setting
Merge pull request #1164 from dimagi/app-secure-url

Secure submissions app setting (Preview only!)