Add a macro to display filtered feeds on mail archive topics / mails

Though possible to integrate feeds from the archive in other sites / pages easily (through MailArchive.RemoteIntegration), it would be nice to have a dedicated macro to display selected feeds from the archive.

Something like:

{{mailarchiverss types="proposal" item="topic" nb="10"/}}

The idea behind is to be able to easily create a sort of dashboard of the archive, for example for XWiki mailing-lists it could display last proposals, xwiki farm requests, announcements, and so on...

Note: could be nice also, when adding a new Type of mail, to propose to the admin to publish this type automatically to this dashboard, and so to propose a default dashboard packaged with the application. The default dashboard would only display last topics and last mails.