am/applets: Add Applet superclass to describe a generic applet

Adds an Initialize and Execute methods which are used by the ILibraryAppletAccessor to start and control the applet.

src/core/hle/service/am/applets/applets.cpp

@@ -0,0 +1,29 @@
+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "core/frontend/applets/software_keyboard.h"
+#include "core/hle/service/am/applets/applets.h"
+
+namespace Service::AM::Applets {
+
+std::shared_ptr<Frontend::SoftwareKeyboardApplet> software_keyboard =
+    std::make_shared<Frontend::DefaultSoftwareKeyboardApplet>();
+
+void Applet::Initialize(std::vector<std::shared_ptr<IStorage>> storage) {
+    storage_stack = std::move(storage);
+    initialized = true;
+}
+
+void RegisterSoftwareKeyboard(std::shared_ptr<Frontend::SoftwareKeyboardApplet> applet) {
+    if (applet == nullptr)
+        return;
+
+    software_keyboard = std::move(applet);
+}
+
+std::shared_ptr<Frontend::SoftwareKeyboardApplet> GetSoftwareKeyboard() {
+    return software_keyboard;
+}
+
+} // namespace Service::AM::Applets