Update legislation drafts translatable fields

Updating it required reorganizing the form so translatable fields are
together.

We also needed to add a `hint` option to the form label and input
methods so the hint wouldn't show up for every language.

Finally, the markdown editor needed to use the same globalize attributes
as inputs, labels and hints, which adds a bit of duplication.

app/assets/javascripts/markdown_editor.js.coffee

@@ -3,12 +3,12 @@ App.MarkdownEditor =
   refresh_preview: (element, md) ->
     textarea_content = App.MarkdownEditor.find_textarea(element).val()
     result = md.render(textarea_content)
-    element.find('#markdown-preview').html(result)
+    element.find('.markdown-preview').html(result)
 
   # Multi-locale (translatable) form fields work by hiding inputs of locales
   # which are not "active".
   find_textarea: (editor) ->
-    editor.find('textarea:visible')
+    editor.find('textarea')
 
   initialize: ->
     $('.markdown-editor').each ->
@@ -26,7 +26,7 @@ App.MarkdownEditor =
         return
 
       editor.find('textarea').on 'scroll', ->
-        $('#markdown-preview').scrollTop($(this).scrollTop())
+        editor.find('.markdown-preview').scrollTop($(this).scrollTop())
 
       editor.find('.fullscreen-toggle').on 'click', ->
         editor.toggleClass('fullscreen')