Openra: Togglable option to automatically show transport unit load

[FRenzy-OpenRA]

Suggestion :
Having a togglable option (similar to the togglable health bar), allowing the user to show the "load bar" of transport units, without the need to select them.
The bar would only be shown if transport is at least partially loaded.

Could also be useful for spectators, and teammates.

[Smittytron]

Show on mouseover would make sense as well.

[dragunoff]

This could well be added to the existing option. Right now it shows not just health but also construction/training progress and capture progress. Though that might be too much visual clutter.

Having this functionality also makes sense for units with ammo (aircraft, mine-layers, etc).

[pchote]

Related to #5606 - this could use the same tooltip UI.