Extending KNIME Menus and right click context menus

I was working on creating my nodes on knime for some project, I did'nt find any documentation on how we could extend KNIME by adding stuffs to the menu and context menus. OR for example I wanted to extend the import/export functionality of KNIME projects, so that I could convert legacy structures already used in my project to knime projects and vice versa. 

I could still do this with a work around by adding Nodes of export and import operations. But this is not that intuitive