MDL-48798 Statistics: Adding lang string for user activity.

New lang string for 'Activity' (meaning count of user actions) in stats
reports to disambiguate it with 'Activity' (meaning course module).

AMOS BEGIN
 CPY [activity,core],[useractivity,core]
AMOS END

lang/en/moodle.php

@@ -1904,6 +1904,7 @@
 $string['user'] = 'User';
 $string['userconfirmed'] = 'Confirmed {$a}';
 $string['usercurrentsettings'] = 'My profile settings';
+$string['useractivity'] = 'Activity';
 $string['userdata'] = 'User data';
 $string['userdeleted'] = 'This user account has been deleted';
 $string['userdescription'] = 'Description';

lib/statslib.php

@@ -1242,7 +1242,7 @@ function stats_get_parameters($time,$report,$courseid,$mode,$roleid=0) {
         $param->fields = 'sum(stat1+stat2) AS line1';
         $param->stattype = 'activity';
         $param->orderby = 'line1 DESC';
-        $param->line1 = get_string('activity');
+        $param->line1 = get_string('useractivity');
         $param->graphline = 'line1';
         break;
 
@@ -1268,7 +1268,7 @@ function stats_get_parameters($time,$report,$courseid,$mode,$roleid=0) {
                       ) enrolments
                       ON (activity.courseid = enrolments.courseid)
                       ORDER BY line3 DESC';
-        $param->line1 = get_string('activity');
+        $param->line1 = get_string('useractivity');
         $param->line2 = get_string('users');
         $param->line3 = get_string('activityweighted');
         $param->graphline = 'line3';