Add a market/Kleinanzeigen section to WeGlide

[scalvin1]

My idea for the day:
Trying to find/buy/sell equipment and gliders is difficult at the moment. The existing market on segelfl__.de is barely working, has painfully small pictures and has not been improved for decades. Time for a new market, users would love it:
WeGlide probably already has 99% of what is needed to pull this off when you think of it: Photos, stories, regionalization, filtering. (It could almost be done 'as is', i.e. with takeoff point 'market' or something and allowing empty flight data...)