store links with a fallback path

[peter88213]

Currently (v3.2.0), links are stored as paths relative to the project path, if possible.
There should be also a full path (relative to the user's home directory) as a fallback in case the project directory has moved.

Implementation

novxlib

The BasicElement.links dictionary has the short path as key, and the filename as value.
The value could be used for a long path.

nvlib

If the file name is needed, it can be generated with os.split().