Save display count on app exit

[hugeBlack]

It seems that display count is only saved when windows is shutting down and is never read. This PR fixed this issue.

[nomi-san]

This feature is added before the last release, but need an option to allow it works.
These lines were in right place, no need to move them.

parsec-vdd/app/ParsecVDD.cs

Lines 62 to 71 in 271e334

	static async void UpdateRoutine(CancellationToken token)
	{
	// TODO: restore added displays
	//int initialCount = Config.DisplayCount;
	//if (initialCount > 0)
	//{
	// for (int i = 0; i < initialCount; i++)
	// AddDisplay();
	//}

[hugeBlack]

Oh, I missed these lines.