votes: allow admins to remove post votes.

Allow admins to remove votes on posts. This is for fixing vote abuse.

Votes can be removed by going to the vote list on the /post_votes page,
or by clicking on a post's score, then using the "Remove" option in the
"..." dropdown menu next to the vote.

Votes are soft-deleted - they're marked as deleted in the database, but
not fully deleted. Removed votes are only visible to admins, not to
regular users. When a vote is removed by an admin, it leaves a mod
action.

Technically it's possible to undelete votes, but there's no UI for it.

test/unit/post_test.rb

@@ -701,12 +701,12 @@ class PostTest < ActiveSupport::TestCase
             @post.update(tag_string: "aaa fav:self")
             assert_equal(1, @post.reload.score)
             assert_equal(1, @post.favorites.where(user: @user).count)
-            assert_equal(1, @post.votes.positive.where(user: @user).count)
+            assert_equal(1, @post.votes.active.positive.where(user: @user).count)
 
             @post.update(tag_string: "aaa -fav:self")
             assert_equal(0, @post.reload.score)
             assert_equal(0, @post.favorites.count)
-            assert_equal(0, @post.votes.positive.where(user: @user).count)
+            assert_equal(0, @post.votes.active.positive.where(user: @user).count)
           end
 
           should "not allow banned users to fav" do
@@ -1433,11 +1433,12 @@ class PostTest < ActiveSupport::TestCase
         end
       end
 
-      should "not decrement the post's score for basic users" do
+      should "decrement the post's score for basic users" do
         @member = FactoryBot.create(:user)
 
-        assert_no_difference("@post.score") { create(:favorite, post: @post, user: @member) }
-        assert_no_difference("@post.score") { Favorite.destroy_by(post: @post, user: @member) }
+        assert_difference("@post.reload.score", -1) do
+          Favorite.destroy_by(post: @post, user: @user)
+        end
       end
 
       should "not decrement the user's favorite_count if the user did not favorite the post" do
@@ -1565,7 +1566,7 @@ class PostTest < ActiveSupport::TestCase
       post.vote!(1, user)
 
       assert_equal(1, post.reload.score)
-      assert_equal(1, post.votes.count)
+      assert_equal(1, post.votes.active.count)
     end
 
     should "allow undoing of votes" do
@@ -1578,31 +1579,33 @@ class PostTest < ActiveSupport::TestCase
       assert_equal(1, post.score)
       assert_equal(1, post.up_score)
       assert_equal(0, post.down_score)
-      assert_equal(1, post.votes.positive.count)
+      assert_equal(1, post.votes.active.positive.count)
 
-      post.unvote!(user)
+      post.votes.last.soft_delete!
+      post.reload
       assert_equal(0, post.score)
       assert_equal(0, post.up_score)
       assert_equal(0, post.down_score)
-      assert_equal(0, post.votes.count)
+      assert_equal(0, post.votes.active.count)
 
       post.vote!(-1, user)
       assert_equal(-1, post.score)
       assert_equal(0, post.up_score)
       assert_equal(-1, post.down_score)
-      assert_equal(1, post.votes.negative.count)
+      assert_equal(1, post.votes.active.negative.count)
 
-      post.unvote!(user)
+      post.votes.last.soft_delete!
+      post.reload
       assert_equal(0, post.score)
       assert_equal(0, post.up_score)
       assert_equal(0, post.down_score)
-      assert_equal(0, post.votes.count)
+      assert_equal(0, post.votes.active.count)
 
       post.vote!(1, user)
       assert_equal(1, post.score)
       assert_equal(1, post.up_score)
       assert_equal(0, post.down_score)
-      assert_equal(1, post.votes.positive.count)
+      assert_equal(1, post.votes.active.positive.count)
 
       post.reload
       assert_equal(1, post.score)