Support for user permissions

Supporting permissions would be very useful!

you can get permissions with something like:

```sql
SELECT user, host FROM user
foreach {
SHOW GRANTS FOR '$user'@$host
}
```

I guess, ignore certain users (`mysql.sqs`, `rdsadmin`, `root`, the user used by morphism?), etc.

Then add GRANT/REVOKE as necessary.

You can add passwords as you can use the hashed version.