Fixes Vizzuality/cartodb-management#2602
Adds white gradient for the filter section. Increases the size of search form (fixes Vizzuality/cartodb-management#2605)
Merge branch 'develop' of github.com:CartoDB/cartodb20 into develop

* 'develop' of github.com:CartoDB/cartodb20:
  fixed Vizzuality/cartodb-management#2617
  Revert "Memoize (almost) all the things related to visualizations"
  Revert "Optimize affected_visualization retrieval"
  Revert "Do no render related tables in GET /api/v1/viz"
  preparing the ground when visualization won't return the related_tables attribute
  Do no render related tables in GET /api/v1/viz
  fixed Vizzuality/cartodb-management#2607
  Optimize affected_visualization retrieval
  fixes vizzuality/cartodb-management#2463
  Memoize (almost) all the things related to visualizations
  Memoize visualization map