First step in using HorizontalProxyModel to show selected row in properties table.

HorizontalProxyModel now inherits from QIdentityProxyModel which provides a more complete base implementation (maybe to much?)
for now it seems to do what we want, forward relevant signals which the abstract base didn't.
Issues: Properties table needs formatting and shows all rows as columns instead of values of a single row.

pglab/HorizontalProxyModel.cpp

@@ -5,7 +5,7 @@
 
 
 HorizontalProxyModel::HorizontalProxyModel(QObject *parent)
-	: QAbstractProxyModel(parent)
+	: QIdentityProxyModel(parent)
 {
 }