refs #1419 - add 'Remember Me' to Login form; unchecked by default (which is safe by default); small change to core/Cookie.php to allow cookie to expire at end-of-session; shorten persistent cookie life to 14 days

Note: potential compat buster: logme() cookie is no longer persistent


git-svn-id: http://dev.piwik.org/svn/trunk@2901 59fd770c-687e-43c8-a1e3-f5a4ff64c105