Added Callbacks for serverside paging/sorting

Added logic to allow for serverside paging/sorting via external callbacks

example use of serverside paging
totalRows keeps the total number of records to work out the paging, the external API only returns the data required in the current page however it always returns the total amount of records for the query

this.sortGridData = function (headerName, propertyName, descending) {
                that.pagingViewModel.sortByField = propertyName;
                that.pagingViewModel.descending = descending;
                that.getEntries(); //this method calls a external API to refresh the data
            };

            this.refreshGridData = function (pageSize, pageIndex) {
                that.pagingViewModel.pageSize = pageSize;
                that.pagingViewModel.pageIndex = pageIndex;
                that.getEntries(); //this method calls a external API to refresh the data
            };

            this.gridConfig = {
                data: that.journalEntries,
                pageSize: 30,
                columns: [
                    { header: 'Date/Time', property: 'DateUpdated', sortEvent: that.sortGridData },
                    { header: 'Client', property: 'ClientCode', sortEvent: that.sortGridData },
                    { header: 'Activity', property: 'Activity', sortEvent: that.sortGridData },
                    { header: 'Purpose', property: 'Purpose', sortEvent: that.sortGridData },
                    { header: 'Notes', property: 'Notes', sortEvent: that.sortGridData },
                    { header: 'Options', property: '', canSort:false }
                ],
                useServerSidePaging: true,
                totalRows: ko.observable(0),
                refreshData: that.refreshGridData
            };