Add config option to update charset of mysql to utf8mb4

config/config.sample.php

core/register_command.php

lib/private/DB/AdapterMySQL.php

lib/private/DB/ConnectionFactory.php

lib/private/DB/MDB2SchemaReader.php

lib/private/DB/MDB2SchemaWriter.php

lib/private/Repair/Collation.php

lib/private/Server.php

lib/private/Setup/MySQL.php