Reworked config handling and command execution.

I didn't like the repetition of format calls and the requirement that every
function do something to initialize the config.

By creating the 'configured' decorator we automatically initialize a global
configuration based on the first argument to the function (assumed to be a
name).

Some additional configuration was needed based on user input. Using the
'additional_config' context manager we temporarily augment the global
configuration.

This allows all command execution to be executed by dfrun and dfsudo and since
the config is applied to every command there are no more string.format calls
cluttering the code.
Renamed the module so that it can be imported.

I use dashes in the file names often enough to be embarrassed right now.