UTF8 defaults for MySQLDatabase->createDatabase()

Doesn't have much effect in practice, because charset and collation
are already hardcoded on an ALTER TABLE level (field definitions),
which take priority. Since most MySQL installs will still default
to a latin1 encoding, this propagates to the table though,
confusing devs and in some cases causing wrong data.

Example: A MSSQL->MySQL DB migration tool used the table metadata
to determine the charset, creating encoding issues.

In terms of hardcoding, we don't really support anything other than UTF8,
and the field-level settings are already hardcoded.

We should probably remove the field-specific settings and rely
on the DB defaults, but that's a sensitive API change
(need to set on existing DBs during upgrade).
Merge pull request #2326 from chillu/pulls/mysql-create-db-utf8

UTF8 defaults for MySQLDatabase->createDatabase()