Add UI text to indicate [current]/[max] for filtered cargo

[Ripshaft]

Just had neat idea...

Suggestion:
When you set cargo filters on a train, it adds the filtered quantities to the object UI (when you mouse over)

Example:

• New train, 1 engine and 2 cargo wagons. Mouse over the train, wagons - exact same as current.
  In each cargo wagon, set 1 square's filter to 'Plastics'
  Mouseover either cart - shows '0/100 Plastics'
  Mouseover locomotive - shows '0/200 Plastics'

I expect that is enough to illustrate the basic idea, obviously there's some questions as to how to handle inventory of that type that is outside the filters, but there are many potential ways of handling that.


Reasoning:
This would be incredibly useful for doing a quick assessment of the material amounts your train can carry, for using the 'cargo = ' conditional, general assessment or fact-checking when planning material gathering (how many times have you forgotten stack counts for different materials? No more!).
Allows for easy assessment of fill level.
Neato.