Fix ChangeIdAnnotator for "Any Server" option

ChangeIdAnnotator is not working when job is configured with "any server" option. It is preventing the commit message from being displayed in the changes screen since it throws an exception.

First, fixed the provider url to contains the front end url (was always empty) and then reworked the changeIdAnnotator to get the url from the provider which comes from the gerritCause.

This problem was introduced in 2.11.0 so I guess we could release a 2.11.1 with this fix if you want.