Add rendering of PT platforms areas

[Matthias84]

Public transport consists of stops, but also the platforms of stops. This are usually with concrete and maybe with dedicated lines to keep space between passangers and incoming transport vehicles. Some also offer lines dedicated for visual impaired people to find the stop position and find the way away from the platform.

IMHO they cover significant amount of public space and like the already rendered stops they could help consumers to understand the structure of a neighbourhood, central places, ....