Update hard-coded currency UI with currency specific params (#488)

* Update hard-coded currency UI with currency specific params

* Rename extension methods to match currency option names; Move cents extension to numeric class extension

* Use currency's precision to show the cents part in accounts show page

---------

Co-authored-by: Sriram Krishnan <sriram@seafoodsouq.com>

test/initializers/string_extensions_test.rb

@@ -0,0 +1,19 @@
+# test/string_extensions_test.rb
+require "test_helper"
+
+class StringExtensionsTest < ActiveSupport::TestCase
+  test "#unit returns the currency unit for a given currency code" do
+    assert_equal "$", "USD".unit
+    assert_equal "€", "EUR".unit
+  end
+
+  test "#separator returns the currency separator for a given currency code" do
+    assert_equal ".", "USD".separator
+    assert_equal ",", "EUR".separator
+  end
+
+  test "#precision returns the currency's precision for a given currency code" do
+    assert_equal 2, "USD".precision
+    assert_equal 0, "KRW".precision
+  end
+end