Late game transport UI rework: Aerodromes, airports and train stations.

One of the things that I think that can be easily be improved in the late game visualization is to have airports, aerodromes and railway lines way more highlighted.

Here I will collect several suggestions regarding ONLY THE UI, so no balance issues from implementing this. 

 For yields and balance of these districts i heavily suggest to see this other thread: https://community.amplitude-studios.com/amplitude-studios/humankind/ideas/2895-rework-train-stations-and-airports

Starting with aerodromes, they are obviously required for creating and using air units. However, they are difficult to see on the general map, and for example, if you want to create a network of aerodromes to bring aircraft from the cities to the frontlines, it's hard to see where you already placed one. I would suggest that once you click to place the aerodrome district, the other aerodromes already placed would highlight. Alongside with this, I would reccomend that when selecting an air unit, the range radius should be shown in some way, but this might be more difficult to implement. 

A similar approach should be applied to train stations and Airports. When moving units,  airports, Train stations and railway lines showuld be more highlighted than roads and normal districts. This is really important when managing large empires, where  you easily lose track of what you have built. As depicted for aerodromes, When placing a train station or airports, you should be able to see where the other ones are located.

Aside from these UI changes, I would reccomend also to include airport and train routes to the Unit pathfinding, so when I move an unit, they try to use these transports if they are available. However, i know that this is a QOL feature more difficult to  implement, so on this post i wanted to focus more on an easy solution, to give the player a clear view of their transport network.