balancing IN now evens fuel on the IN tanks, OUT on the OUT tanks automatically
"Balance" balances on all or the selected ones if there are any, behaves weird if used on IN/OUT tanks
Merged in BloodyRain2k's changes.

(remote-tracking branch 'remotes/BloodyRain2k/master'
Conflicts: TacFuelBalancer/TacFuelBalancer.cs)
It now shows which stage each part is in.