[explorev2] no bootstrap data, just metadata in exploreV2 (#1827)
[explorev2] no bootstrap data, just metadata in exploreV2 (#1827)

json_data really just returns the *metadata* for the slice, where
get_json returns both the metadata and the data
airbnb/caravel,massgov/incubator-superset,asdf2014/superset,asdf2014/superset,dmigo/incubator-superset,FrederichCheng/incubator-superset,airbnb/superset,apache/incubator-superset,mistercrunch/panoramix,BRD-CD/superset,zhouyao1994/incubator-superset,timifasubaa/incubator-superset,ArijanaBrlek/superset,airbnb/superset,massgov/incubator-superset,zhouyao1994/incubator-superset,timifasubaa/incubator-superset,airbnb/caravel,massgov/incubator-superset,zhouyao1994/incubator-superset,alanmcruickshank/superset-dev,nekia/incubator-superset-dev,SingTel-DataCo/incubator-superset,alanmcruickshank/superset-dev,alanmcruickshank/superset-dev,FrederichCheng/incubator-superset,nekia/incubator-superset-dev,robert-digit/superset,apache/incubator-superset,ArijanaBrlek/superset,alanmcruickshank/superset-dev,zhouyao1994/incubator-superset,robert-digit/superset,mistercrunch/panoramix,nekia/incubator-superset-dev,apache/incubator-superset,asdf2014/superset,massgov/incubator-superset,BRD-CD/superset,dmigo/incubator-superset,FrederichCheng/incubator-superset,airbnb/superset,SingTel-DataCo/incubator-superset,ArijanaBrlek/superset,robert-digit/superset,dmigo/incubator-superset,timifasubaa/incubator-superset,dmigo/incubator-superset,airbnb/caravel,airbnb/superset,timifasubaa/incubator-superset,apache/incubator-superset,nekia/incubator-superset-dev,SingTel-DataCo/incubator-superset,BRD-CD/superset,zhouyao1994/incubator-superset,SingTel-DataCo/incubator-superset,apache/incubator-superset,robert-digit/superset,asdf2014/superset,mistercrunch/panoramix,BRD-CD/superset,airbnb/caravel,mistercrunch/panoramix,ArijanaBrlek/superset,FrederichCheng/incubator-superset