Economy/Hungry autopilot + Higher fuel use rate + pirates intercept the player + ...

<b>DO NOT MERGE BEFORE THOROUGH DISCUSSION!</b>

This is reaction to issue #20 and discussion with @Brianetta in issue #1582. While all my pull requests before were "cosmetic details", only slightly changing something, this pull request changes some important things in the philosophy of the game. It is quite possible, that you will not like it and I'm aware that this is a bit controversial, but I'm sending you this pull request to show you this path that I personally very like. (If you don't like it, simply do not merge it, but I would be very glad for any discussion or remarks.) So, what is it about?

Short list might be:
* Economical autopilot, which will save fuel if low on fuel.
* Hungry autopilot which also saves fuel if low on it, but burns fuel more quickly.
* Both autopilots refuel automatically if there is water in cargo bay.
* Pirates now intercept the player using AICmdFlyTo command invoked by AICmdKill.
* Ship's fuel rates were changed to be higher.

But why?

The idea of issue #20 was, that there will be hungry autopilot and economy autopilot with different fuel consumption. The pirates would use the hungry autopilot to intercept the trading ships running on economy autopilot. But in current version of the game, all the ships have so small fuel use rate that there is no point in saving fuel. So I proposed that the fuel use rate would be higher. It makes sense also from the point of view of physics: if you do the calculations from Tsiolkovsky rocket equation, you find out that the current ships release the propellant by speeds like 1000000 km/s and more, while realistic is far less.  (If you are interested in details, I wrote nice <a href="https://docs.google.com/spreadsheet/ccc?key=0Avf9Om_zOYZPdFVDSUVZZmk5U0M0elFRSXlNQ1d3V1E">excel sheet</a> to do the math - try it!).

So in this proposal, the fuel use rate was calculated in such way, that the propellant escape velocity is similar for all engines. (Smaller for bigger ships, but this is quite arbitrary, I only wanted them to move slower.) This makes sense, because you can always increase total thrust by adding more engine units, but propellant escape velocity depends on technology (fusion engine). If you want to travel fast, you simply must pack with fuel - the limiting factor is always the fuel mass/total mass ratio, not the acceleration. 

So how does typical journey look like in this mod? 
1) hyperspace jump to the system
2) quickly accelerate to the travel speed ~1000 km/s - 4000 km/s
3) change the course carefully, not consume too much fuel, maintain the speed
4) decelerate

I added the pirates intercepting the ship to show, that the AI can navigate with such fuel use rates without problems. Maybe I didn't do it in the most clever way - you tell me. Also, the navigation across different frames must be yet checked, the save files will need a new version. You can try, how it is. (And yes, travelling in 70 AU big star systems IS pain in the ass, but otherwise it's not that bad..).

This is the controversial thread with "all changes included", but I will maintain the issue #1582 independent of the changes in the fuel use rates: it might be good to include economical autopilot even into the original version -- it doesn't slow the player down if it has a lot of fuel, but it will not consume all the fuel and let the player die in uncontrollable ship. So if you don't like this one, you can still merge #1582 and loose nothing.

If you want to give it a shot, try few journeys across Epsilon Eridani/Earth system. Try it again, but pack the whole cargo space with water and see what happens. Then try also the hungry autopilot. And the last: try few journeys to Kaptayn's star or other star and meet the pirates :-)

Thanks for all remarks in advance!

P.S. I do not do this for the sake of "simulation", but more to support the feeling of true cosmic flights. This is why I loved Frontier and definitely love Pioneer.