This removes the global PDF_Password interface that had completely
bitrotted and moves it into the standard misc operation table with a
sensible defualt implementation.
This also cleans up and fixes the gtk frontend implementation of the
pdf password callback so it compiles.
Finally this moves the implementation to a sensible place alongside
the other exporters reducing target makefile complexity futher.
Currently it can only open, display and launch entries in an existing hotlist file.
TODO:
- Generate defualt hotlist when file not found.
- Add hotlist saving.
- Allow adding to hotlist.
- Allow hotlist editing.
- Allow hotlist nodes to be moved by dragging.
- Allow hotlist visit data to be updated.
