Bugzilla plugin is now converted to backend sync service

as the summary, Bugzilla is now a backend sync service. It can be used simply as it was a plugin before. When enable this service, any added task will be handled and attempt to sync bug information from specific related Bugzilla service.

This version works well, but not perfect. I'm being continue to add more features, such as the configuration ability.
You should set title only and only when it needs to be different. Otherwise you create an infinite loop: User changes the task => bugzilla backend is triggered because of the change => bugzilla backend sets the title => bugzilla backend is triggered because of the change => bugzilla backend sets the title => ...