Use utf8_unicode_ci as default collation

I think the default table collation should be set to `utf8_unicode_ci` - it handles properly a much wider array of characters at a minuscule cost to performance.

An import with a default mysql setup will create tables with `utf8_general_ci` collation.

> utf8_general_ci is a legacy collation that does not support expansions, contractions, or ignorable characters. It can make only one-to-one comparisons between characters.
> -- http://dev.mysql.com/doc/refman/5.0/en/charset-unicode-sets.html