Added a common language string 'image'

htdocs/lang/en.utf8/mahara.php

@@ -511,6 +511,7 @@ $string['clamemailsubject'] = '%s :: Clam AV notification';
 $string['clamlost'] = 'Clam AV is configured to run on file upload, but the path supplied to Clam AV, %s, is invalid.';
 $string['clamfailed'] = 'Clam AV has failed to run.  The return error message was %s. Here is the output from Clam:';
 $string['clamunknownerror'] = 'There was an unknown error with clam.';
+$string['image'] = 'Image';
 $string['filenotimage'] = 'The file you uploaded is not valid image. It must be a PNG, JPEG or GIF file.';
 $string['virusfounduser'] = 'The file you have uploaded, %s, has been scanned by a virus checker and found to be infected! Your file upload was NOT successful.';
 $string['virusrepeatsubject'] = 'Warning: %s is a repeat virus uploader.';