UI: Add date/time to log file

Although log files are saved with the date in the name of the log file,
it's also nice to be able to see it inside the log file itself,
especially when uploaded to a text service.

UI/obs-app.cpp

@@ -1232,6 +1232,8 @@ bool OBSApp::OBSInit()
 	obs_apply_private_data(settings);
 	obs_data_release(settings);
 
+	blog(LOG_INFO, "Current Date/Time: %s", CurrentDateTimeString().c_str());
+
 	blog(LOG_INFO, "Browser Hardware Acceleration: %s",
 			browserHWAccel ? "true" : "false");
 #endif