Added unwrap to filter method to make it work with observableArrays

[esbenp]

Added a unwrap to the filter method so it works if an observableArray is passed to the DataTable constructor.

[cmbankester]

Thanks for this PR, but allowing an observableArray to be stored in @rows seems odd, considering @rows is an observableArray itself. I do think we should be using ko.unwrap, though.

[cmckni3]

I found this to be odd as well.

I think we would use ko.unwrap on the places changing the observableArray's value. For example, calling ko.unwrap on the rows local variable in the replaceRows function.

[cmbankester]

@cmckni3 Exactly. Basically anywhere we're calling a ko observable (e.g. this.rows(), this.sortDir(), etc.), we should instead use ko.unwrap (i.e. ko.unwrap(this.rows), ko.unwrap(this.sortDir) respectively).