Gui: several fixes for expression search box:

+ rename method setMatchExact() to setExactMatch()
+ move handling of user-defined parameters to class ExpressionParameter
+ Qt::MatchExactly is not supported by QCompleter, use Qt::MatchStartsWith instead
+ add possibility to change match behaviour via context-menu

src/Gui/DlgPropertyLink.cpp

@@ -76,7 +76,7 @@ DlgPropertyLink::DlgPropertyLink(QWidget* parent)
     ui->typeTree->hide();
     ui->searchBox->installEventFilter(this);
     ui->searchBox->setNoProperty(true);
-    ui->searchBox->setMatchExact(false);
+    ui->searchBox->setExactMatch(Gui::ExpressionParameter::instance()->isExactMatch());
 
     timer = new QTimer(this);
     timer->setSingleShot(true);