Show UI warning to user when they need provider data but have not setup Synth yet (#1926)

* Simplify provider concerns

* Update tests

* Add UI warning for missing Synth key if family requires external data

test/system/imports_test.rb

@@ -52,6 +52,8 @@ class ImportsTest < ApplicationSystemTestCase
   end
 
   test "trade import" do
+    Security.stubs(:search_provider).returns([])
+
     visit new_import_path
 
     click_on "Import investments"

test/system/trades_test.rb

@@ -10,7 +10,7 @@ class TradesTest < ApplicationSystemTestCase
 
     visit_account_portfolio
 
-    Security.stubs(:search).returns([
+    Security.stubs(:search_provider).returns([
       Security.new(
         ticker: "AAPL",
         name: "Apple Inc.",