Update Bootstrap to v4.1, fix chosen.js and pagedown on multiple sites

app/views/exercises/_editor.html.slim

@@ -6,8 +6,7 @@
 - hide_rfc_button = @hide_rfc_button || false
 #editor.row data-exercise-id=@exercise.id data-message-depleted=t('exercises.editor.depleted') data-message-timeout=t('exercises.editor.timeout',  permitted_execution_time: @exercise.execution_environment.permitted_execution_time) data-errors-url=execution_environment_errors_path(exercise.execution_environment) data-submissions-url=submissions_path data-user-id=@current_user.id data-user-external-id=external_user_external_id data-working-times-url=working_times_exercise_path(@exercise) data-intervention-save-url=intervention_exercise_path(@exercise) data-rfc-interventions=show_rfc_interventions data-break-interventions=show_break_interventions data-course_token=@course_token data-search-save-url=search_exercise_path(@exercise)
   div id="sidebar" class=(@exercise.hide_file_tree ? 'sidebar-col-collapsed' : 'sidebar-col') = render('editor_file_tree', exercise: @exercise, files: @files)
-  div id='output_sidebar' class='output-col-collapsed' = render('exercises/editor_output', external_user_id: external_user_id, consumer_id: consumer_id )
-  div id='frames' class='editor-col'
+  div.editor-col.col.p-0 id='frames'
     #editor-buttons.btn-group.enforce-bottom-margin
       = render('editor_button', disabled: true, icon: 'fa fa-ban', id: 'dummy', label: t('exercises.editor.dummy'))
       = render('editor_button', icon: 'fa fa-desktop', id: 'render', label: t('exercises.editor.render'))
@@ -24,6 +23,7 @@
       = t('exercises.editor.lastsaved')
       span
       button style="display:none" id="autosave"
+  div id='output_sidebar' class='output-col-collapsed' = render('exercises/editor_output', external_user_id: external_user_id, consumer_id: consumer_id )
 
 
 = render('shared/modal', id: 'comment-modal', title: t('exercises.implement.comment.request'), template: 'exercises/_request_comment_dialogcontent')