[change] Adjust settings to use new bw2data.projects method

[dgdekoning]

This MR is related to https://github.com/cauldron/activity-browser/issues/3.

The wasm branch in bw2data contains the new method that handles changing the brightway data directory.

Checklist

• [x] Keep pull requests small so they can be easily reviewed.
• [x] Update the documentation, please follow the numpy style guide
• [ ] Update tests.
• [x] Categorize the PR by setting a good title and adding one of the labels: bug, feature, ui, change, documentation, breaking, ci as they show up in the changelog
• [x] Link this PR to related issues.

[dgdekoning]

Included in this MR are:

• Changes to the code to make use of the new method (part 1 of the issue)
• Changes to settings.py to replace the existing method with direct calls to bw2data for the _base_data_dir (part 2 of the issue).
• Additional type-hinting and doc-string updates.
• Changing from os use to pathlib.Path, except for one instance where os.path.normpath is used as there is no functionally similar call in pathlib.