move call-center form stats to new SQL form index

Actually, that table is intuitively upside-down, but documented as such:

> operator precedences in Python, *from lowest precedence (least binding) to highest precedence (most binding)*

Emphasis added. So `%` take precedence in this case. This is, this is equivalent:

```py
TABLE_PREFIX = ('%s_' % settings.CTABLE_PREFIX) if hasattr(settings, 'CTABLE_PREFIX') else ''
```

NOT this:

```py
TABLE_PREFIX = '%s_' % (settings.CTABLE_PREFIX if hasattr(settings, 'CTABLE_PREFIX') else '')
```