various preset updates :)

added stripe preset, which makes spinning plaid patterns
adjusted twinkle's handling of dense starfields
added a param for fungus's black/erase color.
added color params for spiral (slow - some rework re: colorfade /color
mapping is probably in order)
added missing parameter for radial gradient's luminance channel
Merge branch 'master' of https://github.com/craftyjon/firemix