* Moving 'segments' definition to a hook that each plugin can listen to. So far only referers, user country and visit server time define segments.
 * Fixing issue related to column sorting. By default it was sorting by nb_uniq_visitors, now sorting by nb_visits (because unique visitors column is not displayed in the goals table)

git-svn-id: http://dev.piwik.org/svn/trunk@2309 59fd770c-687e-43c8-a1e3-f5a4ff64c105