Always add relative references from the Wysiwyg link / image wizards

Currently, the references (to linked pages and images) added by the Wysiwyg link / images wizard use full references such as (after transformation in wiki syntax):

[[label>>xwiki:Main.WebHome]] 
[[image:xwiki:Main.WebHome@attachedImage.png]]

They shoud be minimal in the sense of containing as less redundant information as possible (no space & wiki if the linked page is in the same space, no wiki if the linked page is in the same wiki, etc, no wiki, space, page if the linked file is attached to the current page):

[[link to page in the same wiki>>Space.Page]]
[[link to page in the same space>>PageName]]
[[link to file attached to this page>>attach:filename]]
[[image:attachedImage.png]]