Annotations application should not overwrite the default skin

The annotations application contains the XWiki.DefaultSkin page (for the annotationsinline.vm template used to generate the annotations tab), which, on installing / packing, will overwrite the default skin.

This is not good because:

• it can reset modifications made by developers to the skin (when installed on an existing wiki),
• if, on a default enterprise, the user changes the skin to be used, annotations tab will stop working which is not a very intuitive side-effect,
• when packed in the default enterprise .xar it collides with the XWiki.DefaultSkin installed by the administration application,
• it's good in general that applications don't affect existing documents or rely on a specific state of a document, but only add their own.

Starting with the 2.4 platform version, the annotationsinline.vm template will be shipped in the platform (see XWIKI-5360).