Use utf8 charset for MySQL tables

See [FS#91](http://bugs.crash-override.net/index.php?do=details&task_id=91).

If no character set/collation is specified when creating a table, the database (or server) default is used. MySQL uses the latin1 charset with the latin1_swedish_ci collation by default -- this means that in the worst case (if the adminstrator didn't choose a more sane default charset), characters not contained in the latin1 charset will be garbled in the address books. Explicitly choosing an Unicode charset and collation makes sure that these characters are stored correctly in all cases.

I chose the utf8_unicode_ci collation because even if it is slower than the utf8_general_ci collation, it is more accurate (which seems appropriate for an address book). The [MySQL manual](http://dev.mysql.com/doc/refman/5.6/en/charset-unicode-sets.html) has more information.