Path List

This allows you to configure the path list used by Opus directly, without
having to worry about where the path list is going to be inherited from.

The 'Use Opus internal path list' gadget will enable the list, the Clear
button the right will clear all paths from the list.

You can select a path in the list and use Delete to remove it, conversely
you can use the Add button and the string gadget or folder button next to
it to add a path.