Add CommunitySolution

* Also slightly refactor some JS files

app/models/community_solution.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+class CommunitySolution < ApplicationRecord
+  belongs_to :exercise
+  has_many :community_solution_locks
+  has_many :community_solution_contributions
+  has_and_belongs_to_many :users, polymorphic: true, through: :community_solution_contributions
+  has_many :files, class_name: 'CodeOcean::File', through: :community_solution_contributions
+
+  def to_s
+    "Gemeinschaftslösung für #{exercise}"
+  end
+end

app/models/community_solution_contribution.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class CommunitySolutionContribution < ApplicationRecord
+  include Creation
+  include Context
+
+  belongs_to :community_solution
+  belongs_to :community_solution_lock
+
+  validates :proposed_changes, boolean_presence: true
+  validates :timely_contribution, boolean_presence: true
+  validates :autosave, boolean_presence: true
+  validates :working_time, presence: true
+end

app/models/community_solution_lock.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class CommunitySolutionLock < ApplicationRecord
+  include Creation
+
+  belongs_to :community_solution
+  has_many :community_solution_contributions
+
+  validates :locked_until, presence: true
+
+  def active?
+    Time.zone.now <= locked_until
+  end
+
+  def working_time
+    ActiveSupport::Duration.build(locked_until - created_at)
+  end
+end