[Feature] Make flux:flexform.grid.column name localizable

Currently a ``flux:flexform.grid.column`` name is not localizable like all the other containers. This adds the ability to localize the name:

```xml
flux.FlexformID.columns.YourColumnName
```

For this to work the optional label for the view helper has to be ``NULL`` on default. (Which doesn't matter much because it will fallback to ``name`` if no ``label`` is present).