UI: Move obs startup/shutdown to obs-app.cpp

Now that we aren't dependent upon a window for our context, we can
safely move the obs context creation/destruction to obs-app.cpp, and use
the OBSContext helper class to automatically shut down obs.

obs/obs-app.cpp

@@ -592,6 +592,7 @@ bool OBSApp::OBSInit()
 			config_save(globalConfig);
 		}
 
+		obs_startup(locale.c_str());
 		mainWindow = new OBSBasic();
 
 		mainWindow->setAttribute(Qt::WA_DeleteOnClose, true);

obs/obs-app.hpp

@@ -20,6 +20,7 @@
 #include <QApplication>
 #include <QTranslator>
 #include <QPointer>
+#include <obs.hpp>
 #include <util/lexer.h>
 #include <util/util.hpp>
 #include <string>
@@ -59,6 +60,7 @@ private:
 	std::string		       theme;
 	ConfigFile                     globalConfig;
 	TextLookup                     textLookup;
+	OBSContext                     obsContext;
 	QPointer<OBSMainWindow>        mainWindow;
 
 	bool InitGlobalConfig();

obs/window-basic-main.cpp

@@ -841,8 +841,6 @@ void OBSBasic::OBSInit()
 	if (ret <= 0)
 		throw "Failed to get scene collection json file path";
 
-	if (!obs_startup(App()->GetLocale()))
-		throw "Failed to initialize libobs";
 	if (!InitBasicConfig())
 		throw "Failed to load basic.ini";
 	if (!ResetAudio())
@@ -1114,8 +1112,6 @@ OBSBasic::~OBSBasic()
 	 * expect or want it to. */
 	QApplication::sendPostedEvents(this);
 
-	obs_shutdown();
-
 	config_set_int(App()->GlobalConfig(), "General", "LastVersion",
 			LIBOBS_API_VER);