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);