HaikuDepot: Update for web-app API changes.

 * Category identifyers are lower-case, we can use the "name" facility which
   already existed for this purpose and simply iterate the list of known
   categories.
 * The getBulkPkg method now takes the architectures as a list as well,
   helps with finding the right package in case there is a mix of
   architectures across the requested package names.