[GH-198] Change default MySQL table collation to utf8_unicode_ci

This issue is created automatically through a Github pull request on behalf of VladanStef:

Url: https://github.com/doctrine/dbal/pull/198

Message:

I think default table collation should be changed to `utf8_unicode_ci`, as it handles properly a much wider array of characters (Cyrillic, for example) at a generally negligible cost of performance.

`utf8_general_ci` simply does not work properly with too many languages and should be avoided as a default.