Version 1.3.7

- New sprites for Letalium and Enriched Letalium (credits go to Jani from Jani's Shipyard).
- Slight buff to advanced ion beam prisms. Now slightly more efficient when combining beams.
- Larger common asteroids with rare raw materials from ETTM will now be a bit more common in tier 10 and higher star systems (still pretty rare though).
- Minor tweaks here and there.