Use text_area instead of cktext_area

We're going to change CKEditor to an inline editor, and the "ckeditor"
gem doesn't provide an option to do so.

Since using `cktext_area` would automatically generate a "classic"
iframe CKEditor, we need to use `text_area` and load the editor using
JavaScript. Personally I prefer this option anyway.

Note in the jQuery selector we need to use `textarea.html-area`; using
just `.html-area` would fail if there's an error message associated to
the textarea, since Rails will add the `.html-area` class to the error
message.

app/assets/javascripts/application.js

@@ -55,6 +55,7 @@
 //= require checkbox_toggle
 //= require markdown-it
 //= require markdown_editor
+//= require html_editor
 //= require cocoon
 //= require answers
 //= require questions
@@ -114,6 +115,7 @@ var initialize_modules = function() {
   App.SocialShare.initialize();
   App.CheckboxToggle.initialize();
   App.MarkdownEditor.initialize();
+  App.HTMLEditor.initialize();
   App.LegislationAdmin.initialize();
   App.LegislationAllegations.initialize();
   App.Legislation.initialize();