Implement forum topic voting and tag change pruning (#3580)

app/models/forum_post_vote.rb

@@ -0,0 +1,44 @@
+class ForumPostVote < ApplicationRecord
+  belongs_to_creator
+  belongs_to :forum_post
+  validates :creator_id, uniqueness: {scope: :forum_post_id}
+  validates :score, inclusion: {in: [-1, 0, 1]}
+  scope :up, -> {where(score: 1)}
+  scope :down, -> {where(score: -1)}
+  scope :by, ->(user_id) {where(creator_id: user_id)}
+  scope :excluding, ->(user_id) {where("creator_id <> ?", user_id)}
+
+  def up?
+    score == 1
+  end
+
+  def down?
+    score == -1
+  end
+
+  def meh?
+    score == 0
+  end
+
+  def fa_class
+    if score == 1
+      return "fa-thumbs-up"
+    elsif score == -1
+      return "fa-thumbs-down"
+    else
+      return "fa-meh"
+    end
+  end
+
+  def vote_type
+    if score == 1
+      return "up"
+    elsif score == -1
+      return "down"
+    elsif score == 0
+      return "meh"
+    else
+      raise
+    end
+  end
+end