PLAT-364 Add getCategoryByName back to WikiFactoryHub

This adds the getCategoryByName method back to WikiFactoryHub. There are some existing calls to this method that have not been removed so we need to continue to support this interface.

/cc @Wikia/platform-team @owend @inez 
Technically I don't think it's necessary because there are 3 distinct return values from `strcasecmp` but I went ahead and added it in 65afb24. It's better to be conservative when checking anything against 0 in PHP.