Add the information about which categories contain which pbi types and allow the user to retrieve these simple lists.

Usage:
"pbi list [all/graphical/text/server]cats"
so "pbi list servercats" will list all the categories with server PBI's listed.

NOTE: the "pbi list cats" syntax has been changed to "pbi list allcats"
Merge branch 'master' of github.com:pcbsd/pcbsd