Icons for filters

[JoselleAstrid]

At minimum, have icons for machine filters, since the current FZC has those. Next priority is probably icons for platform filters (SNES, Wii U VC, etc.) since the forum-based WR tables had those. Then possibly other types of filters.

On the DB level, I guess any filter should be allowed to have icons, and they should be optional in case it's not feasible to give all of them icons. (Of note though, GuyPerfect is providing us icons for all the possible GX custom machines, so at least that group would be complete!)

Considerations:

• Image storage and image serving. Storing as blobs in the database is probably viable, but not sure if that has benefits over just storing a path/URL in the DB and storing the images elsewhere. Serving from static URLs would be good since these icons are unlikely to change, and are good to cache in the browser.
• Image resolution(s). The current icons are rather small (about 20 pixels on one side) and aren't always easy on the eyes because of that.
• When should the UI display filter text, filter icon, or both? (This is more of an fzerocentral-web concern though.)