New functionality "Function/Post"

Current behavior
Currently a post like "Chairman" can only be displayed in the LoS via structure level. This is a problem if something like party membership is also modeled via structure level and should be displayed at the same time.
Posts don't typically have speaking times, also it would maybe be good for people to be able to select the function in which they want to speak themselves

Wanted behavior
Posts wouldn't typically have speaking times, also it would maybe be good for people to be able to select the function in which they want to speak themselves, as such the structure level feature doesn't really fit the bill. There should be a new model post that fills these requirements. A participant should be able to have multiple posts and he should be able to select one of them, when he puts himself on the LoS.

Start by examining the existing structure-level implementation in the TypeScript webclient and how participants add themselves to the LoS. The work is done when participants can have multiple posts, select one while joining the LoS, and posts do not inherit structure-level speaking-time behavior.