Install and use ToastUi markdown editor

Replace all usages of pagedown-bootstrap editor with the new editor.
Add styles to ensure the editor preview matches the final output.

app/views/tips/_form.html.slim

@@ -1,3 +1,10 @@
+- content_for :head do
+  // Force a full page reload, see https://github.com/turbolinks/turbolinks/issues/326.
+     Otherwise, code might not be highlighted correctly (race condition)
+  meta name='turbolinks-visit-control' content='reload'
+  - append_javascript_pack_tag('toast-ui')
+  - append_stylesheet_pack_tag('toast-ui')
+
 = form_for(@tip, builder: PagedownFormBuilder) do |f|
   = render('shared/form_errors', object: @tip)
   .mb-3
@@ -5,7 +12,7 @@
     = f.text_field(:title, class: 'form-control', required: false)
   .mb-3
     = f.label(:description, class: 'form-label')
-    = f.pagedown :description, input_html: {preview: true, rows: 5}
+    = f.pagedown :description
   .mb-3
     = f.label(:file_type_id, t('activerecord.attributes.file.file_type_id'), class: 'form-label')
     = f.collection_select(:file_type_id, @file_types, :id, :name, {include_blank: true}, class: 'form-control')