Update helper.php for preserving UPPER / lower case in column names

#IMPORTANT: ONLY the "Update helper.php" is meant here - sorry, due to not carefully thinking automatic blew up that request erroneously with things that have to do nothing with pull requesting ...

#What: Skipped utf8_strtolower() for 'key' in function _column() 
#Why: Preserve UPPER / lower case in column names when editing dataentry with the built-in custom entry editor
#Note: Seems that utf8_strtolower() is used here to avoid trouble with allowed characters in SQLite column names?