Changed propertyMapping 'column' to 'name'

In according to Doctrine's documentation, the column name should use attribute 'name' instead of 'column',

e.g.

```
/**
* @ORM\Column(name="my_field")
*/
protected $field;
```

instead of

```
/**
* @ORM\Column(column="my_field")
*/
protected $field;
```

See http://docs.doctrine-project.org/en/latest/reference/annotations-reference.html#annref-column