Allow List (AL) - The list of users who the user has explicitly
allowed to see state change notifications and establish
client-to-client sessions via a Switchboard Server.
Block List (BL) - The list of users who the user has explicitly
prevented from seeing state change notifications and
establishing client-to-client sessions via a Switchboard Server.
Given this location, for instance "pub.gale@ofb.net", construct
the list of candidate key names for this location:
pub.gale@ofb.net
pub.*@ofb.net
*@ofb.net
There will always be N+1 candidate key names for a location with
N local parts (e.g., "pub" and "gale").
Thrown by CommandInterface.execute() method when a command is
supported by the particular CommandInterface instance, but failed
for some reason when it was attempted.