Fix project dataset saving when rpath is used

[zhiltsov-max]

Summary

Closes #602

• Changed how dataset path is stored in ProjectDataset to use only the source directory. This follows the logic of how project contains sources and allows to save/export/patch project datasets in essential way.

How to test

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below)

# Copyright (C) 2021 Intel Corporation
#
# SPDX-License-Identifier: MIT