refs #3158: remember selected metric in multi row evolution as part of the url...

refs #3158: remember selected metric in multi row evolution as part of the url - using the back and forward buttons after picking different metrics is possible now

git-svn-id: http://dev.piwik.org/svn/trunk@7182 59fd770c-687e-43c8-a1e3-f5a4ff64c105