refactor sessiondialog a bit

- made code more local by moving clicked slot to lambda
 - use class initializations
 - move default value inside the constructor to reduce arguments

Change-Id: I98735a0b4c69ea538ed1af6133ef1054039a1b11
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/projectexplorer/sessionmodel.cpp

@@ -224,7 +224,7 @@ void SessionModel::switchToSession(const QString &session)
 
 void SessionModel::runNewSessionDialog(const QString &suggestedName, std::function<void(const QString &)> createSession)
 {
-    SessionNameInputDialog newSessionInputDialog(SessionManager::sessions(), nullptr);
+    SessionNameInputDialog newSessionInputDialog;
     newSessionInputDialog.setWindowTitle(tr("New Session Name"));
     newSessionInputDialog.setValue(suggestedName);