Convert 4byte chars into the corresponding HTML entity (MySQL-only) - added an hidden setting to prevent the conversion, to be used if the utf8mb4 charset is used

Signed-off-by: emanuele <emanuele45@gmail.com>
Fix php_to8bit to handle 4byte chars - fix preview of messages containing 4byte chars

Signed-off-by: emanuele <emanuele45@gmail.com>