Idea: Don't show save icon in top header bar

[thdk]

Idea is that we do not need an explicit save action.
Having an explicit save icon gives the user the impression that clicking back does NOT save the item, while it DOES save...

Now, clicking the back icon in the navigation bar also saves the item. So we have two actions (back button icon + save icon) to save an item.

Everything should be saved when leaving a detail screen (project detail, user detail, registration detail) or when pressing ctrl + s.