Fixes bug that prevented adding layers to a visualization from the dashboard
Merge branch 'feature/CDB-237' of github.com:CartoDB/cartodb into feature/CDB-237

* 'feature/CDB-237' of github.com:CartoDB/cartodb:
  Add ssl_allowed to WMS proxy
Merge remote-tracking branch 'origin/feature/CDB-237' into release/2.5.2