i18n: Add concept of translatable content

bootstrap.php

include/ajax.config.php

include/ajax.i18n.php

include/class.config.php

include/class.dept.php

include/class.i18n.php

include/class.translation.php

include/staff/department.inc.php

include/staff/header.inc.php

include/staff/template.inc.php

scp/ajax.php

scp/css/jquery.translatable.css

scp/js/jquery.translatable.js