Something changed in LESS that was causing our .icon() mixins to

cross-contaminate, meaning that some rules for defining .rb-icon-*

were also being duplicated as .datagrid-icon-*. This change wraps our

djblets styles to ensure that the .icon() mixin stays in a very

limited scope.

Loaded the Review Board dashboard and saw that the datagrid icons were

no longer messed up.