factorise ajax call

 _makeConversionAjaxCall(data, successCallback, failureCallback) {
        var originCurrency = this.state.originCurrency;
        var destCurrency = this.state.destinationCurrency;

        var payload = {
            originAmount: data.newValue || this.state.originAmount,
            destAmount: data.newValue || this.state.destAmount,
            originCurrency: originCurrency,
            destCurrency: destCurrency,
            calcOriginAmount: false
        }

        // determine whether we need to calc origin or dest amount
        if (data.currentlyEditing === 'dest') {
            payload.calcOriginAmount = true
        }

        // ajax call for destination amount
        // originCurrency, destCurrency, originAmount
        axios.get('/api/conversion', {
            params: payload
        })
        .then((resp) => {
            successCallback(resp.data);
        })
        .catch(failureCallback);

    }