Add a "Close version" property (BB-3124)

Assuming a case where my milestone is 1.0.0 and let's say I have some 1.0.0-BETA and RC planned to reach my milestone or some internal releases. Right not the "version" attribute is not clear if it refers to the version where the bug is found or the version where the bug is closed (or am I misusing the version and milestone properties?). I think a "Close version" property would help clearly stating what version is affected by a bug (version property) and where it has been fixed (close version). It would be also easy to provide a changelog to the users simply querying by "Close version". As fas as I remember also JIRA has this approach.