Better sorting for Fuel combobox

[PBAKER26]

Made a CompareTo method for the Fuel class for better control over sorting. Makes it easier to read up and down the fuel chain when planning reactors.
Fuel selection combobox will now use this sorting method.

[hellrage]

Hello! Sorry about the delay. The fuels are already sorted by criticality (see

NC-Reactor-Planner/NC Reactor Planner/Palette.cs

Line 298 in fe3f95c

fuelList.Sort((x, y) => x.Value.CriticalityFactor.CompareTo(y.Value.CriticalityFactor));

), which is what I generally use.
There is, however, a request for different sorting criteria, so I'll merge it when I have the time to implement those as well, based on your commit!
Thank you for contributing :)