CoreTiming: Data structure cleanup

Replace adhoc linked list with a priority heap. Performance
characteristics are mostly the same, but is more cache friendly.

[Priority Queues have O(log n) push/pop compared to the linked
list's O(n) push/O(1) pop but the queue is not big enough for
that to matter, so linear is faster over linked. Very slight gains
when framelimit is unlimited (Wind Waker), 1900% -> 1950%]

Source/Core/Core/State.cpp

@@ -70,7 +70,7 @@ static Common::Event g_compressAndDumpStateSyncEvent;
 static std::thread g_save_thread;
 
 // Don't forget to increase this after doing changes on the savestate system
-static const u32 STATE_VERSION = 55;
+static const u32 STATE_VERSION = 56;
 
 // Maps savestate versions to Dolphin versions.
 // Versions after 42 don't need to be added to this list,