Unify ISOFile (wx) with GameFile (Qt) and put it in UICommon

The original reason I wanted to do this was so that we can replace
the Android-specific code with this in the future, but of course,
just deduplicating between DolphinWX and DolphinQt2 is nice too.

Fixes:

- DolphinQt2 showing the wrong size for split WBFS disc images.

- DolphinQt2 being case sensitive when checking if a file is a DOL/ELF.

- DolphinQt2 not detecting when a Wii banner has become available
after the game list cache was created.

Removes:

- DolphinWX's ability to load PNGs as custom banners. But it was
already rather broken (see https://bugs.dolphin-emu.org/issues/10365
and https://bugs.dolphin-emu.org/issues/10366). The reason I removed
this was because PNG decoding relied on wx code and we don't have any
good non-wx/Qt code for loading PNG files right now (let's not use
SOIL), but we should be able to use libpng directly to implement PNG
loading in the future.

- DolphinQt2's ability to ignore a cached game if the last modified
time differs. We currently don't have a non-wx/Qt way to get the time.

Source/Core/DolphinQt2/MenuBar.cpp

@@ -34,10 +34,11 @@
 #include "DiscIO/WiiSaveBanner.h"
 
 #include "DolphinQt2/AboutDialog.h"
-#include "DolphinQt2/GameList/GameFile.h"
 #include "DolphinQt2/QtUtils/ActionHelper.h"
 #include "DolphinQt2/Settings.h"
 
+#include "UICommon/GameFile.h"
+
 MenuBar::MenuBar(QWidget* parent) : QMenuBar(parent)
 {
   AddFileMenu();
@@ -593,8 +594,9 @@ void MenuBar::InstallWAD()
 
   QMessageBox result_dialog(this);
 
-  if (GameFile(wad_file).Install())
+  if (WiiUtils::InstallWAD(wad_file.toStdString()))
   {
+    Settings::Instance().NANDRefresh();
     result_dialog.setIcon(QMessageBox::Information);
     result_dialog.setText(tr("Successfully installed this title to the NAND."));
   }
@@ -698,12 +700,12 @@ void MenuBar::NANDExtractCertificates()
   }
 }
 
-void MenuBar::OnSelectionChanged(QSharedPointer<GameFile> game_file)
+void MenuBar::OnSelectionChanged(std::shared_ptr<const UICommon::GameFile> game_file)
 {
-  bool is_null = game_file.isNull();
+  const bool game_selected = !!game_file;
 
-  m_recording_play->setEnabled(!Core::IsRunning() && !is_null);
-  m_recording_start->setEnabled(!Movie::IsPlayingInput() && !is_null);
+  m_recording_play->setEnabled(game_selected && !Core::IsRunning());
+  m_recording_start->setEnabled(game_selected && !Movie::IsPlayingInput());
 }
 
 void MenuBar::OnRecordingStatusChanged(bool recording)