Allow configuring adding new ingredients and exercises

[rolandgeider]

trafficstars

From user feedback: it should be possible to configure the application so that users can add exercises or ingredients directly, without going through an administrator, this can be a new variable in the config app. We can have different settings (for each the ingredients and the exercises), e.g.

• users can't submit anything
• users submit things and an admin has to check (current behaviour)
• users submit directly, admins just get notified

[dtopal]

Can I try working on this?