removed unused list function `messages_xml` from packages/kujua-sms.
fixed forms export for district admin filtering #421

Cleaned up the data records/forms export code.

Added new endpoint for exporting forms data:

    /exports/forms/{form}

This new endpoint requires `startkey` and `endkey` parameters to return
output.

For example, to get all valid CSAC form submissions before
Date(1385852400000) you would use these params:

```
{
    "startkey": "[true,\"CSAC\",{}]",
    "endkey": "[true,\"CSAC\",1385852400000]",
    "include_docs": "true",
    "descending": "true",
    "tz": "-60",
    "reduce": "false",
    "format": "csv"
}
```

This would give you the same output except filtered by district:

```
{
    "startkey": "[true,\"d049925d-72da-063b-24ff6532734a81b0\",\"CSAC\",{}]",
    "endkey": "[true,\"d049925d-72da-063b-24ff6532734a81b0\",\"CSAC\",1385852400000]",
    "dh_name": "Ilorin",
    "tz": "-60",
    "reduce": "false",
    "format": "csv"
}
```

You can pass the param structure below to `querystring.stringify` and
append to the URL to get a valid export file.

Changed to using `data_records` view now so we can remove these extra
views and endpoints which don't make much sense anymore.  This should
improve performance of the database.

```
    {
        from: '/:form/data_records.csv',
        to: '_list/data_records_csv/data_records_valid_by_district_form_and_reported_date'
    },
    {
        from: '/:form/data_records.xml',
        to: '_list/data_records_xml/data_records_valid_by_district_form_and_reported_date'
    },
    {
        from: '/form_data_records.xml',
        to: '_list/data_records_xml/data_records_by_form_valid_and_reported_date'
    },
    {
        from: '/form_data_records.csv',
        to: '_list/data_records_csv/data_records_by_form_valid_and_reported_date'
    },

```

TODO:

Remove the above view/lists and update related tests.

Possibly redirect old URLs or return a backwards incompatible warning on
how to rewrite them.