Add absolute path functionality

[AdrianRoggenbach]

Add possibility to use absolute paths for models and training datasets. This make the use of the package much more flexible, since the user can use the functionality of the package while keeping his own folder structure in the project.

I realized the need for this when implementing the algorithm in my own pipeline.

I will implement this probably next week.

[AdrianRoggenbach]

Addressed in commit 404f405 but not fully tested yet.

[AdrianRoggenbach]

Tested.