Add markdown cache columns to the database, but don't use them yet

This commit adds a number of _html columns and, with the exception of Note,
starts updating them whenever the content of their partner fields changes.

Note has a collision with the note_html attr_accessor; that will be fixed later

A background worker for clearing these cache columns is also introduced - use
`rake cache:clear` to set it off. You can clear the database or Redis caches
separately by running `rake cache:clear:db` or `rake cache:clear:redis`,
respectively.

1 files changed, 1 insertions, 1 deletions

diff --git a/spec/models/service_spec.rb b/spec/models/service_spec.rb
index ed1bc9271ae..43937a54b2c 100644
--- a/spec/models/service_spec.rb
+++ b/spec/models/service_spec.rb
@@ -238,7 +238,7 @@ describe Service, models: true do
       it "updates the has_external_issue_tracker boolean" do
         expect do
           service.save!
-        end.to change { service.project.has_external_issue_tracker }.from(nil).to(true)
+        end.to change { service.project.has_external_issue_tracker }.from(false).to(true)
       end
     end