Refactor zones

- Rename "zonefile_setting" to "zone"
- Remove version

#475

spec/features/admin/dns/zones/edit_spec.rb

@@ -0,0 +1,29 @@
+require 'rails_helper'
+
+RSpec.feature 'Editing zone in admin area' do
+  given!(:zone) { create(:zone) }
+
+  background do
+    sign_in_to_admin_area
+  end
+
+  scenario 'updates zone' do
+    open_list
+    open_form
+    submit_form
+
+    expect(page).to have_text(t('admin.dns.zones.update.updated'))
+  end
+
+  def open_list
+    click_link_or_button t('admin.menu.zones')
+  end
+
+  def open_form
+    click_link_or_button t('admin.dns.zones.zone.edit_btn')
+  end
+
+  def submit_form
+    click_link_or_button t('admin.dns.zones.form.update_btn')
+  end
+end