Custom VCF INFO/FORMAT - Custom Columns

As part of #41. Requires #1240 to be completed

We'd like to be able to view custom VCF info/filter/format columns in the analysis grid

I don't think you'd want to adjust your CustomColumnsCollection every time a new VCF shows up, so maybe make that have 3x columns (info/format/filter) you can drag around like we currently handle the single "sample level" column:

```
In [29]: VariantGridColumn.objects.filter(annotation_level='S').values()
Out[29]:
```

We probably want to keep the old sample level stuff separate until we fully prise it apart from the new info fields.

Then, we need to work out a method to decide what to display.

Eg I can imagine that you perhaps only want to show the "CN" (copy number) field and that's it

Perhaps you want to configure it like columns/tags then it gets assigned based on eg VCF "source"