Add support for recaptcha during the create account flow

If the feature is enabled and recaptcha keys are given in config, then a recaptcha box is displayed in the UI when creating a user and a recaptcha response code *must* be sent with the create API call for it to succeed.

endpoints/common.py

@@ -220,6 +220,7 @@ def render_page_template(name, route_data=None, **kwargs):
                                        enterprise_logo=app.config.get('ENTERPRISE_LOGO_URL', ''),
                                        mixpanel_key=app.config.get('MIXPANEL_KEY', ''),
                                        munchkin_key=app.config.get('MARKETO_MUNCHKIN_ID', ''),
+                                       recaptcha_key=app.config.get('RECAPTCHA_SITE_KEY', ''),
                                        google_tagmanager_key=app.config.get('GOOGLE_TAGMANAGER_KEY', ''),
                                        google_anaytics_key=app.config.get('GOOGLE_ANALYTICS_KEY', ''),
                                        sentry_public_dsn=app.config.get('SENTRY_PUBLIC_DSN', ''),