Address more review comments

* Make Validation a singleton instead
* Wording changes for error messages
* Smart pointers for Ui members
* Other minor nitpicks

src/citra_qt/main.cpp

@@ -133,8 +133,6 @@ GMainWindow::GMainWindow() : config(new Config()), emu_thread(nullptr) {
 
     SetupUIStrings();
 
-    setWindowTitle(QString("Citra %1| %2-%3")
-                       .arg(Common::g_build_name, Common::g_scm_branch, Common::g_scm_desc));
     show();
 
     game_list->LoadCompatibilityList();