Problem: Find a way on how to add a new navigation link to navigation structure from the given assign submission/feedback plugin into activities node.

Currently navigation structure is loaded to main navigation block from the given activity (= module). The callback is a method:

_extend_navigation(), e.g. forum_extend_navigation

There is a way to give the local plugins a chance to include some navigation if they want, but this deals with /local folder and adds content to main navigation block, not module settings block.

Solution: add a function, which calls