[dbal] Store id (uuid) as binary data.

[makasim]

It turned out that Doctrine uses string type internally for most of the drivers (except Postgres)

As written here it is much better to store UUIDs as binary data.

I propose changing id column to be binary and adding a new with a string representation (for a human).

[makasim]

http://mysqlserverteam.com/storing-uuid-values-in-mysql-tables/

[makasim]

PR is opened