Establish patterns for command-specific configuration.

[tshowers-bt]

We should support configuration settings for each command. Currently we support a single option at "Peer.WatchIntervalSeconds" to specify the refresh interval when peer show -w is run. We should come up with a convention for command-specific configuration going forward; maybe using the command name as a prefix (1), or making sections under "Peer" for each command, or something else. We should also consider automatic generation of a complete configuration file and patterns for configuration error detection/reporting.

(1) Currently there is no watch command but it is planned

Related:
#32
#88
#111
#145