add grey boost icons, generate css for boost shop

#150

add boost icon in grey versions (60% lightness seemed to match other
grey icons)

add addCSSRule function for dynamic css generation ability

add generation of boost shop icon css rules
Update boosts.js

Flipside fix
Merge pull request #562 from LucidCrux/icons_in_shop

Grey Boost Shop icons, dynamic css rule creation
Merge pull request #563 from mart0258/patch-1

Update boosts.js