Change round trip random seed generation (or german docs)

Currently, the round trip random seed is a value between 0 and 90, and most docs except the german reflect that.

However, programmatically, this could be any integer, and I don't see a reason for it to be limited to between 0 and 90 (as that will only generate 91 different routes). I liked the approach of the old client, to increase the seed by one with every click of `randomize` and make earlier routes available by having back and forth buttons to increase/decrease the seed.

This hides the randomness abstraction from the user, while everybody willing could have a look at the request to see the number that was actually used, especially since it cannot be set by the user anyways.

While this is not changed, maybe the german docs should be to reflect the current behaviour