Allow user to change name of migrations with config

Tiny update, but some user's might find it useful if they are anal about such things. Allows the change of the name the migrations report.

```
'migrations' => array(
    'name'       => 'My Custom Name',
    'directory'  => '/database/migrations',
    'table_name' => 'migration_versions'
)
```

The name defaults to *Doctrine Sandbox Migrations* if no config item is present.