WIP: Fix tests
The change in 8c6f0eac has effects on tests (although the project test was already failing before that). This branch tries to fix them again.
- make unidirectional the first edge type, since that was the default before
- when loading, skip all the default edge types
The problem with skipping all the default edge types is that they might exist in current files as well, with different settings. The loader probably needs to be much smarter.