Don't export non-modified synthetics

[felixlinker]

Synthetic module properties, e.g. kinetic resistance, are always exported. Only do this, when they have actually been modified.

[felixlinker]

Actually, since we also must support SLEF in future, it might be beneficial to not export anything that doesn't deviate from the blueprint's progress. This would (in practice) also lead to much shorter URLs for coriolis.