Thread scopes through #matches?. #454.

Also add an apply_to_mentions attribute on Glitch::KeywordMute, which is
used to calculate scope.  Next up: additions to the test suite to
demonstrate how scoping works.

spec/models/glitch/keyword_mute_helper_spec.rb

@@ -2,6 +2,8 @@ require 'rails_helper'
 
 RSpec.describe Glitch::KeywordMuteHelper do
   describe '#matches?' do
+    Unscoped = Glitch::KeywordMute::Scopes::Unscoped
+
     let(:alice) { Fabricate(:account, username: 'alice').tap(&:save!) }
     let(:helper) { Glitch::KeywordMuteHelper.new(alice) }
 
@@ -9,42 +11,42 @@ RSpec.describe Glitch::KeywordMuteHelper do
       status = Fabricate(:status, text: '<addr>uh example</addr>')
       Glitch::KeywordMute.create!(account: alice, keyword: 'addr')
 
-      expect(helper.matches?(status)).to be false
+      expect(helper.matches?(status, Unscoped)).to be false
     end
 
     it 'ignores properties of HTML tags in status text' do
       status = Fabricate(:status, text: '<a href="https://www.example.org">uh example</a>')
       Glitch::KeywordMute.create!(account: alice, keyword: 'href')
 
-      expect(helper.matches?(status)).to be false
+      expect(helper.matches?(status, Unscoped)).to be false
     end
 
     it 'matches text inside HTML tags' do
       status = Fabricate(:status, text: '<p>HEY THIS IS SOMETHING ANNOYING</p>')
       Glitch::KeywordMute.create!(account: alice, keyword: 'annoying')
 
-      expect(helper.matches?(status)).to be true
+      expect(helper.matches?(status, Unscoped)).to be true
     end
 
     it 'matches < in HTML-stripped text' do
       status = Fabricate(:status, text: '<p>I <3 oats</p>')
       Glitch::KeywordMute.create!(account: alice, keyword: '<3')
 
-      expect(helper.matches?(status)).to be true
+      expect(helper.matches?(status, Unscoped)).to be true
     end
 
     it 'matches &lt; in HTML text' do
       status = Fabricate(:status, text: '<p>I &lt;3 oats</p>')
       Glitch::KeywordMute.create!(account: alice, keyword: '<3')
 
-      expect(helper.matches?(status)).to be true
+      expect(helper.matches?(status, Unscoped)).to be true
     end
 
     it 'matches link hrefs in HTML text' do
       status = Fabricate(:status, text: '<p><a href="https://example.com/it-was-milk">yep</a></p>')
       Glitch::KeywordMute.create!(account: alice, keyword: 'milk')
 
-      expect(helper.matches?(status)).to be true
+      expect(helper.matches?(status, Unscoped)).to be true
     end
   end
 end