Fixes selection filter to support null and empty values. Enables the filters but disables the module in the lateral pane.
Merge branch 'develop' of github.com:CartoDB/cartodb20 into develop

* 'develop' of github.com:CartoDB/cartodb20:
  fixed finally private_tables user paramater
  fixed user tables privacy
  Vizjson API endpoint working with and without ssl
  Changes default varnish purge command
  Handle special user permissions on commercial cartodb deployments