Remove void return type on constructors

... so that code completion works when instantiating a new instance of the following classes:

org.jivesoftware.xiff.auth.Anonymous

org.jivesoftware.xiff.auth.Plain

org.jivesoftware.xiff.bookmark.BookmarkManager

org.jivesoftware.xiff.bookmark.BookmarkPrivatePayload

org.jivesoftware.xiff.bookmark.GroupChatBookmark

org.jivesoftware.xiff.bookmark.UrlBookmark

org.jivesoftware.xiff.core.JID

org.jivesoftware.xiff.data.im.RosterItemVO

org.jivesoftware.xiff.data.privatedata.PrivateDataExtension

org.jivesoftware.xiff.events.BookmarkChangedEvent

org.jivesoftware.xiff.events.BookmarkRetrievedEvent

I think that covers all of the classes in the current source that have voids on their constructors.

Once they are removed, you will get code hints when creating a new instance of that class.