Feature request: optionally de-orbit old satellites

[amedee]

Okay, story goes like this.

Your very first SCANsat satellite is low tech, did a >95% LoRes scan of Kerbin, has barely enough fuel to do an inclination change to get that final 5% over the poles, and doesn't have enough solar panels and batteries to keep working 100% of the time when going to Kerbin's night side. It also doesn't have a long range antenna so you can't re-use it as a relay satellite in your CommNet.
You've completed it's contract and it's now effectively End Of Life and cluttering Kerbin's orbit.

Later in the game, you get a new contract, for a Hires scan of Kerbin. As an optional parameter of the contract, you can de-orbit the old satellite and let it burn up in the atmosphere, so that you get magnificent fireworks (and maybe get some money and a few science points).

How to do this:

• The first contract needs to define a unique Vessel Key in the contract parameters.
• The second contract needs to have an optional parameter VesselDestroyed for the earlier Vessel Key.

When hard coded, it would be something like this:

LoRes contract:

	PARAMETER
	{
		// Named for the Scottish physicist who predicted the existence of electromagnetic waves.
		name = Maxwell1
		type = VesselParameterGroup

		define = Maxwell I
		
		PARAMETER
		{
			name = ReachState
			type = ReachState
			targetBody = Kerbin
			situation = ORBITING
		}
	}

HiRes contract:

	PARAMETER
	{
		name = OrbitEndGrp
		type = All

		title = De-Orbit Maxwell I, our first SCANSat satellite 
		optional = True
		completedMessage = Well done, the old satellite has burned up in the atmosphere.
		
		rewardScience = 4.0
		rewardFunds = 5000.0
	
		PARAMETER
		{
			name = OrbitEnd
			type = VesselParameterGroup
			
			vessel = Maxwell I
			
			PARAMETER
			{
				name = VesselDestroyed
				type = VesselDestroyed
			}
		}
	}

Alternatively, these could also just be separate standalone mini-contracts that ask nothing more than to de-orbit satellites that have scanned >95%.

I've been trying to grok the Official SCANsat contract configs but I can't really find where and how to do this.