Add "Navigate" menu

[tibirna]

There are hidden actions "Previous", "Next", "Previous Marked" and "Next Marked" that are not shown anywhere in the main app. menus, although they are quite useful.

TODO: Add a "Navigate" menu and add in it explicit items for "Previous", "Next", "Previous Marked" and "Next Marked". Also, move the "Back" and "Forward" actions from "View" menu to the new "Navigate" menu, where they will make more sense.

[eraxillan]

Well, is this issue still actual? I was unable to find hidden actions mentioned in the code: "Previous", "Next", "Previous Marked" and "Next Marked".
Even work "marked" mentioned only in status message.