Update mysql to use `utf8_unicode_ci` collation by default

MySQL's default collation for utf8 is `utf8_general_ci`, which is
apparently more performant but less correct than `utf8_unicode_ci`. A
default install should be more correct than fast, so this change
explicitely sets the collation to be `utf8_unicode_ci`.

One can check the default character set and collation by issuing the
following query on the client:

    show variables like "%character%";show variables like "%collation%";

Further Reading
---------------

- [Server Character Set and Collation](https://dev.mysql.com/doc/refman/5.5/en/charset-server.html)
- [StackOverflow discussion](http://stackoverflow.com/questions/3513773/change-mysql-default-character-set-to-utf8-in-my-cnf)