Provide alternative implementation of external_source_visualization
Provide alternative implementation of external_source_visualization

to use the new AR hierarchy.

I believe they are only used from specs. See this file:

    ./spec/models/user_table_shared_examples.rb

But I'd say it is better to wait for the removal of the ::UserTable
model to tackle that issue.

CartoDB/cartodb,CartoDB/cartodb,CartoDB/cartodb,CartoDB/cartodb,CartoDB/cartodb