Sphinx: drop attributes for skills, instead show icon on result to indicate flyability

[Artefact2]

One Sphinx attribute per skill is terrible design.

Not only is it very memory hungry (and we're starting to see the effects on Tetroxide), it requires a full reindex after each patch (because they usually add new skills).

Another solution instead is to either

1. Store a list of required skills in ONE Sphinx attribute (not sure if it will reduce the memory usage by a lot)
2. Don't store skills in Sphinx, instead cache required skills in formatLoadoutGridLayout() (with pehaps a custom attribute, and add a hook to see if current character, as of rendering time, can fly it or not).