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/exercises/_form.html.slim

@@ -3,6 +3,8 @@
      Otherwise, code might not be highlighted correctly (race condition)
   meta name='turbolinks-visit-control' content='reload'
   - append_javascript_pack_tag('sortable')
+  - append_javascript_pack_tag('toast-ui')
+  - append_stylesheet_pack_tag('toast-ui')
 
 - execution_environments = ExecutionEnvironment.where.not(file_type_id: nil).select(:file_type_id, :id)
 - file_types = FileType.where.not(file_extension: nil).select(:file_extension, :id)
@@ -18,7 +20,7 @@
     .help-block.form-text == t('.hints.internal_title')
   .mb-3
     = f.label(:description, class: 'form-label')
-    = f.pagedown :description, input_html: {preview: true, rows: 10}
+    = f.pagedown :description
   .mb-3
     = f.label(:execution_environment_id, class: 'form-label')
     = f.collection_select(:execution_environment_id, @execution_environments, :id, :name, {include_blank: t('exercises.form.none')}, class: 'form-control')

app/views/proxy_exercises/_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(@proxy_exercise, multipart: true, builder: PagedownFormBuilder) do |f|
   = render('shared/form_errors', object: @proxy_exercise)
   .mb-3
@@ -5,7 +12,7 @@
     = f.text_field(:title, class: 'form-control', required: true)
   .mb-3
     = f.label(:description, class: 'form-label')
-    = f.pagedown :description, input_html: {preview: true, rows: 10}
+    = f.pagedown :description
   .mb-3
     = f.label(:algorithm, class: 'form-label')
     = f.collection_select(:algorithm, ProxyExercise.algorithms.map {|algorithm, _id| [t("activerecord.attributes.proxy_exercise.algorithm_type.#{algorithm}"), algorithm] }, :second, :first, {}, class: 'form-control form-control-sm')

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')