XWIKI-1454: Split XWiki's maven2 remote repository into 3: snapshots, releases and externals
XWIKI-1454: Split XWiki's maven2 remote repository into 3: snapshots, releases and externals

* Added externals/ repository
* Removed definition of external repos as we don't need them anymore (now that we're asking users to define the repos in their settings.xml files)

git-svn-id: cfa2b40e478804c47c05d0f328c574ec5aa2b82e@3811 f329d543-caf0-0310-9063-dda96c69346f

xwiki/xwiki-platform,pbondoer/xwiki-platform,pbondoer/xwiki-platform,xwiki/xwiki-platform,xwiki/xwiki-platform,pbondoer/xwiki-platform,xwiki/xwiki-platform,pbondoer/xwiki-platform,pbondoer/xwiki-platform,xwiki/xwiki-platform