[Request] Fuel onboard check func. [Implemented on 0.2.0.0]

[OAL853 Nick Papandreou]

For flights in the economic model and when the flight is not a free one (bull3=true in reports table).

When the user press the start flight button, a check routine should check if the fuel loaded on the aircraft is more or equal to the fuel onboard the specific aircraft in the dispatch office.
If it isn't, ACARS should not let the user start the flight and display the appropriate message.

This would disallow pilots from emptying the aircraft of fuel when loading less than the aircraft has in our dispatch office and help get rid of negative "fuelbought" values often shown in many pireps.