TrainingPeaks PWX support L/R balance

.. on import and export, using the "pwrright" element.

.. this is not part of the public PWX schema but has
   been used by ipbike when writing PWX, and may or may
   not be supported by TrainingPeaks.com

src/PwxRideFile.cpp

@@ -220,6 +220,15 @@ PwxFileReader::PwxFromDomDoc(QDomDocument doc, QStringList&) const
                 //       the TP upload web-service happy with zero values
                 if (add.watts == 1) add.watts = 0.0;
             } else add.watts = 0.0;
+            // lrbalance
+            QDomElement lrbalance = node.firstChildElement("pwrright");
+            if (!lrbalance.isNull()) {
+                if (add.watts == 0) {
+                   add.lrbalance = 50.0;
+                } else {
+                    add.lrbalance =(add.watts-lrbalance.text().toDouble())/add.watts*100.0;
+                }
+            } else add.lrbalance = 0.0;
             // torq
             QDomElement torq = node.firstChildElement("torq");
             if (!torq.isNull()) add.nm = torq.text().toDouble();
@@ -831,6 +840,14 @@ PwxFileReader::writeRideFile(Context *context, const RideFile *ride, QFile &file
                 pwr.appendChild(text);
                 sample.appendChild(pwr);
             }
+            // lrbalance
+            if (ride->areDataPresent()->lrbalance) {
+                int rwatts = point->watts ? (point->watts - (point->watts * (point->lrbalance/100))) : 0;
+                QDomElement lrbalance = doc.createElement("pwrright");
+                text = doc.createTextNode(QString("%1").arg(rwatts));
+                lrbalance.appendChild(text);
+                sample.appendChild(lrbalance);
+            }
             // torq
             if (ride->areDataPresent()->nm) {
                 QDomElement torq = doc.createElement("torq");