Fix and enable feature Persistent settings

* Reuse existing steps where possible
* Rename steps file to match convention
* Moved unrelated steps to a new file
* Added wait for saving

https://mingle.corp.wikimedia.org/projects/internationalization/cards/3822

Bug: 56885
Change-Id: I480058430696579947187265b940ea46156f1519

tests/browser/features/step_definitions/panel_steps.rb

@@ -31,7 +31,10 @@ When(/^I close the panel to discard the changes$/) do
 end
 
 When(/^I apply the changes$/) do
-	on(PanelPage).panel_button_apply_element.click
+	on(PanelPage) do |page|
+		page.panel_button_apply_element.click
+		page.language_settings_dialog_element.wait_while_present
+	end
 end
 
 Then(/^I can disable input methods$/) do