This requires us to pass an active fit to use as a base for the modules, as the format does not include ship information. Features:
* If active fit has modules, makes a new fit using same ship
* Does basic dummy checking. As the format doesn't include ship info, it will probably be common for someone to accidentally try to import a Legion fit to a Rifter by mistake. Import logic checks module legality for fit and, if fails, silently halts import without saving.
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