Allow for searching on specified fields instead of entire object

Hi,

I have a datagrid bound to a complex business object, and only a few properties are shown in the grid.
One of the use-cases is the table-wide search on words and parts of words.

The 'problem' is that koGrid seems to check ALL properties in the associated model, instead of just the ones that are shown. This leads to unexpected results, because some rows don't 'visually' contain the search words specified.

Wouldn't it be a good addition if we could specify which properties that have to be included in the search, instead of scanning the entire object for properties?

```
if (!condition.column) {
for (var prop in item) {
if (item.hasOwnProperty(prop)) {
var pVal = ko.utils.unwrapObservable(item[prop]);
if (pVal && condition.regex.test(pVal.toString())) {
return true;
}
}
}
return false;
}
```

Kr
Sander

Start with the table-wide search branch shown in the issue and inspect how the grid's visible columns are configured. Determine how callers can select searchable properties, then verify that searches match only those properties instead of hidden fields.

Written by the indexing model from the issue text.