NEW hooks replacethemelink (header_links.php) and replacethemesbacklink (themes.php)

git-svn-id: http://svn.resourcespace.org/svn/resourcespace@5578 c08608d7-6e46-0410-86ca-f2a6f1370df5
FIX issue when system has languages disabled with custom content.
    Now it picks up the content based on the defaultlanguage


git-svn-id: http://svn.resourcespace.org/svn/resourcespace@5579 c08608d7-6e46-0410-86ca-f2a6f1370df5