Create mockups for multimodal trips entry

[codingfabi]

^When we want to create the possibility to make request emissions for multimodal trips, we need to give the option to add multiple steps to a trip in the frontend. This is can not be trivially added to the existing page, therefor we need a design.

[sarahmadeleine]

Mockups are here: https://docs.google.com/presentation/d/1TZRZZ58mIiAhWESRnMhUpu9pTMA1_ehDg3tm6JJFMrg/edit#slide=id.g1b0ba1f02c0_0_95

note that we also changed some labels