Extended Exercises by worktime, difficulty and tags, added ProxyExercises as prework for recommendations

Tags can be added to exercises in the edit view. Tags can monitored under /tags.
Added the concept of ProxyExercises which are a collection of Exercises. They can be found under /proxy_exercises
Added Interventions as prework to show interventions later to the user.
Added exercise/[:id]/working_time to return the working time of the user in this exercise and the average working time of all users in this exercise

app/views/exercises/_editor.html.slim

@@ -21,4 +21,4 @@
       button style="display:none" id="autosave"
 
 
-= render('shared/modal', id: 'comment-modal', title: t('exercises.implement.comment.request'), template: 'exercises/_request_comment_dialogcontent')
+= render('shared/modal', id: 'comment-modal', title: t('exercises.implement.comment.request'), template: 'exercises/_request_comment_dialogcontent')

app/views/exercises/_form.html.slim

@@ -32,6 +32,25 @@
     label
       = f.check_box(:allow_auto_completion)
       = t('activerecord.attributes.exercise.allow_auto_completion')
+  .form-group
+    = f.label(t('activerecord.attributes.exercise.difficulty'))
+    = f.number_field :expected_difficulty, in: 1..10, step: 1
+  .form-group
+    = f.label(t('activerecord.attributes.exercise.worktime'))
+    = f.number_field "expected_worktime_minutes", value: @exercise.expected_worktime_seconds / 60, in: 1..1000, step: 1
+  h2 Tags
+  .table-responsive
+    table.table
+      thead
+        tr
+          th = t('activerecord.attributes.exercise.selection')
+          th = sort_link(@search, :title, t('activerecord.attributes.tag.name'))
+          th = t('activerecord.attributes.tag.difficulty')
+        = collection_check_boxes :exercise, :tag_ids, @exercise_tags, :tag_id, :id do |b|
+          tr
+            td = b.check_box
+            td = b.object.tag.name
+            td = number_field "tag_factors[#{b.object.tag.id}]", :factor, :value => b.object.factor, in: 1..10, step: 1
   h2 = t('activerecord.attributes.exercise.files')
   ul#files.list-unstyled.panel-group
     = f.fields_for :files do |files_form|

app/views/exercises/implement.html.slim

@@ -22,3 +22,4 @@
     #questions-column
       #questions-holder data-url="#{qa_url}/qa/index/#{@exercise.id}/#{@user_id}"
     = qa_js_tag
+

app/views/exercises/index.html.slim

@@ -16,6 +16,9 @@ h1 = Exercise.model_name.human(count: 2)
         th = sort_link(@search, :execution_environment_id, t('activerecord.attributes.exercise.execution_environment'))
         th = t('.test_files')
         th = t('activerecord.attributes.exercise.maximum_score')
+        th = t('activerecord.attributes.exercise.tags')
+        th = t('activerecord.attributes.exercise.difficulty')
+        th = t('activerecord.attributes.exercise.worktime')
         th
           = t('activerecord.attributes.exercise.public')
           - if policy(Exercise).batch_update?
@@ -29,6 +32,9 @@ h1 = Exercise.model_name.human(count: 2)
           td = link_to_if(exercise.execution_environment && policy(exercise.execution_environment).show?, exercise.execution_environment, exercise.execution_environment)
           td = exercise.files.teacher_defined_tests.count
           td = exercise.maximum_score
+          td = exercise.exercise_tags.count
+          td = exercise.expected_difficulty
+          td = (exercise.expected_worktime_seconds / 60).ceil
           td.public data-value=exercise.public? = symbol_for(exercise.public?)
           td = link_to(t('shared.edit'), edit_exercise_path(exercise)) if policy(exercise).edit?
           td = link_to(t('.implement'), implement_exercise_path(exercise)) if policy(exercise).implement?

app/views/exercises/show.html.slim

@@ -19,6 +19,9 @@ h1
 = row(label: 'exercise.allow_auto_completion', value: @exercise.allow_auto_completion?)
 = row(label: 'exercise.embedding_parameters') do
   = content_tag(:input, nil, class: 'form-control', readonly: true, value: embedding_parameters(@exercise))
+= row(label: 'exercise.difficulty', value: @exercise.expected_difficulty)
+= row(label: 'exercise.worktime', value: "#{@exercise.expected_worktime_seconds/60} min")
+= row(label: 'exercise.tags', value: @exercise.exercise_tags.map{|et| "#{et.tag.name} (#{et.factor})"}.sort.join(", "))
 
 h2 = t('activerecord.attributes.exercise.files')