Fix various UI bugs in the RealFuelsWindow

[periodically-makes-puns]

I'd separate these but they're each like 10 lines at most

• Rescaling a tank with a locked resources should now also scale unlocked resources to compensate for the additional needed/unused volume. Failing to do this led to tanks being overutilised if a resource was locked and the tank was later downsized.
• Adding a resource now reads the Volume rather than the Percentage. Should resolve Requested and Allocated "fuel" value do not match, potential Floating Point issue? #369. This does open up the issue in the opposite direction, technically.
• The UI window should now allow typing when editing the resources of a part that is currently in symmetry. We only allow one part to call ShowGUI and the rest from the symmetry counterparts are suppressed. There's still a lot of weirdness around parts in symmetry, mainly involving resources seemingly being duplicated, so this is by no means a complete fix.

[periodically-makes-puns]

Fixed a couple things pointed out by siimav. Unlocked tanks scaling up is intentional, but we do also scale empty volume now.

To cover the default case, if the percentage field is 100% then we propagate that over to the Amount field (if it's not active), otherwise we propagate the Amount field to the percentage field.

Locks are still a mess and I feel like it needs a rewrite to be inherent to the tank so that it's not dependent on the UI being open. I'm not currently willing to work on that.

[siimav]

This does not build

[periodically-makes-puns]

I got sidetracked for a bit, but I think I covered everything. The extra decimal point does sort of exacerbate the existing width issue for certain mixes (I stare at the Valois with its 4-resource mix) which is not ideal...