Limit scope of icon CSS wildcards to icon-spree-
Limit scope of icon CSS wildcards to icon-spree-

The existing "icon-" wildcards wound up blowing up all of my font awesome stuff in my existing store.  I 'fixed' it locally by cloning this file and changing like 23 to "icon-spree-".  I feel like this is maybe a useful addition to everyone and not just for me.

Thanks for the addon!

Fixes #134

wuboy0307/solidus_social,groundctrl/spree_social,wuboy0307/solidus_social,supherman/spree_social,DynamoMTL/spree_social,denniscastro/spree_social,ramkumar-kr/spree_social,sunny2601/spree_social,gogo52cn/spree_social,gogo52cn/spree_social,spark-solutions/spree_social,gogo52cn/spree_social,denniscastro/spree_social,spree-contrib/spree_social,habib136888/spree_social,sunny2601/spree_social,groundctrl/spree_social,supherman/spree_social,sunny2601/spree_social,ramkumar-kr/spree_social,DynamoMTL/spree_social,paywithamazon/spree_social,rogelio-meza-t/spree_social,groundctrl/spree_social,paywithamazon/spree_social,spark-solutions/spree_social,rogelio-meza-t/spree_social,ramkumar-kr/spree_social,denniscastro/spree_social,solidusio-contrib/solidus_social,solidusio-contrib/solidus_social,spree-contrib/spree_social,habib136888/spree_social,wuboy0307/solidus_social,rogelio-meza-t/spree_social,DynamoMTL/spree_social,spree-contrib/spree_social,solidusio-contrib/solidus_social,supherman/spree_social,habib136888/spree_social,spark-solutions/spree_social