Fixes plus sign in public_table page
Merge branch 'develop' of github.com:CartoDB/cartodb20 into develop

* 'develop' of github.com:CartoDB/cartodb20:
  Table model refactor, fixes some specs
  Locks rack version and updates json version
  Fixes regexp to catch extensions on content-disposition http header
  Updates more gems
  Updates newrelic gem
  Fixes some importer specs
  WIP Refactoring DataImport
  Stop using User#tables_count
  Updates the debugger gem
  remove CartoDB layer logo within app + test added
  hidden 'Powered by CartoDB logo in app map'
  fixed README removing an unnecessary title
  new copy for users with infinite quota
  removed CartoDB2.0 welcome message