docview: removed second constants unit - we only need one
Move constants to constants unit
docview: assign own help file for future dialog help.
debug support
docview: updated todo list file
docview: Implements the Bookmark Maintenance form.

We can now Jump To bookmark, rename bookmarks, delete bookmarks etc.
docview: update help file - bookmarks functionality is now fully implemented
docview: Help button in Notes dialog is now functional.