write catalog now writes relative paths per default

[francescalb]

It is now possible to choose to write abslute paths when writing catalog, but relative paths to current folder are default.

Description:

Type of change:

• Bug fix.
• New feature.
• Documentation update.

Checklist:

This checklist can be used as a help for the reviewer.

• Is the code easy to read and understand?
• Are comments for humans to read, not computers to disregard?
• Does a new feature has an accompanying new test (in the CI or unit testing schemes)?
• Has the documentation been updated as necessary?
• Does this close the issue?
• Is the change limited to the issue?
• Are errors handled for all outcomes?
• Does the new feature provide new restrictions on dependencies, and if so is this documented?

Comments:

[jesper-friis]

Looks good, but haven't tested it... Take a look at the comments and apply those that make sense.