Add support for highlighting categories

Needs Core's I60e6b19d3b59ebf9bb45cc61d16936dfc7e4c708 to do anything.

DEPLOYMENT: Performance will be improved by an in place index rebuild
after this is deployed but it isn't required.
Change-Id: I91c795cb6276a68e646ab4d86942d34e02b26ffe
Merge "Add support for highlighting categories"