Add Site Setting to use HTML from incoming email when available. (#4236)

spec/components/email/receiver_spec.rb

@@ -171,6 +171,18 @@ describe Email::Receiver do
       expect(topic.posts.last.raw).to eq("This is the *text* part.")
     end
 
+    it "prefers html over text when site setting is enabled" do
+      SiteSetting.incoming_email_prefer_html = true
+      expect { process(:text_and_html_reply) }.to change { topic.posts.count }
+      expect(topic.posts.last.raw).to eq('This is the <b>html</b> part.')
+    end
+
+    it "uses text when prefer_html site setting is enabled but no html is available" do
+      SiteSetting.incoming_email_prefer_html = true
+      expect { process(:text_reply) }.to change { topic.posts.count }
+      expect(topic.posts.last.raw).to eq("This is a text reply :)")
+    end
+
     it "removes the 'on <date>, <contact> wrote' quoting line" do
       expect { process(:on_date_contact_wrote) }.to change { topic.posts.count }
       expect(topic.posts.last.raw).to eq("This is the actual reply.")