Remove Synth Finance references (#47)

* Remove Synth Finance integration

* Linter noise

* Fix failing (old) test, use it for Twelve Data

---------

Signed-off-by: Juan José Mata <juanjo.mata@gmail.com>

app/models/security/combobox_option.rb

@@ -0,0 +1,13 @@
+class Security::ComboboxOption
+  include ActiveModel::Model
+
+  attr_accessor :symbol, :name, :logo_url, :exchange_operating_mic, :country_code
+
+  def id
+    "#{symbol}|#{exchange_operating_mic}"
+  end
+
+  def to_combobox_display
+    "#{symbol} - #{name} (#{exchange_operating_mic})"
+  end
+end