Fix generation of icons.css, so that SUI icons don't override it
Fix generation of icons.css, so that SUI icons don't override it

switch-education/pxt,playi/pxt,Microsoft/pxt,Microsoft/pxt,Microsoft/pxt,switchinnovations/pxt,switch-education/pxt,playi/pxt,switchinnovations/pxt,switch-education/pxt,Microsoft/pxt,switch-education/pxt,playi/pxt,playi/pxt,switchinnovations/pxt,Microsoft/pxt,switchinnovations/pxt,switch-education/pxt