Allow TL4 users to accept answers (configurable via site setting)

config/locales/server.en.yml

@@ -1,6 +1,7 @@
 en:
   site_settings:
     allow_solved_on_all_topics: "Allow users to select solutions on all topics (by default you control this by editing categories)"
+    accept_all_solutions_trust_level: "Minimum trust level required to accept solutions on any topic (even when not OP)"
   reports:
     accepted_solutions:
       title: "Accepted solutions"

config/settings.yml

@@ -2,3 +2,6 @@ plugins:
   allow_solved_on_all_topics:
     default: false
     client: true
+  accept_all_solutions_trust_level:
+    default: 4
+    client: true

plugin.rb

@@ -193,7 +193,8 @@ after_initialize do
     def can_accept_answer?(topic)
       allow_accepted_answers_on_category?(topic.category_id) && (
         is_staff? || (
-          authenticated? && !topic.closed? && topic.user_id == current_user.id
+          authenticated? && ((!topic.closed? && topic.user_id == current_user.id) ||
+                            (current_user.trust_level >= SiteSetting.accept_all_solutions_trust_level))
         )
       )
     end