Add destroy rake task

Adds several rake tasks to delete users, topics, pm's and site stats so
that you can have a fresh site but maintain site settings and category
structure.

app/services/destroy_task.rb

@@ -0,0 +1,90 @@
+## Because these methods are meant to be called from a rake task
+#   we are capturing all log output into a log array to return
+#   to the rake task rather than using `puts` statements.
+class DestroyTask
+  def self.destroy_topics(category)
+    c = Category.find_by_slug(category)
+    log = []
+    return "A category with the slug: #{category} could not be found" if c.nil?
+    topics = Topic.where(category_id: c.id, pinned_at: nil).where.not(user_id: -1)
+    log << "There are #{topics.count} topics to delete in #{category} category"
+    topics.each do |topic|
+      log << "Deleting #{topic.slug}..."
+      first_post = topic.ordered_posts.first
+      if first_post.nil?
+        return log << "Topic.ordered_posts.first was nil"
+      end
+      system_user = User.find(-1)
+      log << PostDestroyer.new(system_user, first_post).destroy
+    end
+    log
+  end
+
+  def self.destroy_topics_all_categories
+    categories = Category.all
+    log = []
+    categories.each do |c|
+      log << destroy_topics(c.slug)
+    end
+    log
+  end
+
+  def self.destroy_private_messages
+    pms = Topic.where(archetype: "private_message")
+    current_user = User.find(-1) #system
+    log = []
+    pms.each do |pm|
+      log << "Destroying #{pm.slug} pm"
+      first_post = pm.ordered_posts.first
+      log << PostDestroyer.new(current_user, first_post).destroy
+    end
+    log
+  end
+
+  def self.destroy_groups
+    groups = Group.where(automatic: false)
+    log = []
+    groups.each do |group|
+      log << "destroying group: #{group.id}"
+      log << group.destroy
+    end
+    log
+  end
+
+  def self.destroy_users
+    log = []
+    users = User.where(admin: false, id: 1..Float::INFINITY)
+    log << "There are #{users.count} users to delete"
+    options = {}
+    options[:delete_posts] = true
+    current_user = User.find(-1) #system
+    users.each do |user|
+      begin
+        if UserDestroyer.new(current_user).destroy(user, options)
+          log << "#{user.username} deleted"
+        else
+          log << "#{user.username} not deleted"
+        end
+      rescue UserDestroyer::PostsExistError
+        raise Discourse::InvalidAccess.new("User #{user.username} has #{user.post_count} posts, so can't be deleted.")
+      rescue NoMethodError
+        log << "#{user.username} could not be deleted"
+      end
+    end
+    log
+  end
+
+  def self.destroy_stats
+    ApplicationRequest.destroy_all
+    IncomingLink.destroy_all
+    UserVisit.destroy_all
+    UserProfileView.destroy_all
+    user_profiles = UserProfile.all
+    user_profiles.each do |user_profile|
+      user_profile.views = 0
+      user_profile.save!
+    end
+    PostAction.unscoped.destroy_all
+    EmailLog.destroy_all
+  end
+end