Is your feature request related to a problem? Please describe.
Taken from #903, it would be nice to have an option to MPF.Check and MPF.CLI to show saved config options.

Describe the solution you'd like
git uses git config list

get_iplayer uses get_iplayer --prefs-show.

I like the get_iplayer method, as it shows you the filename the config came from. You can also do:

Config Options:
 --prefs-add                                         Add/Change specified saved user or preset options
 --prefs-clear                                       Remove *ALL* saved user or preset options
 --prefs-del                                         Remove specified saved user or preset options
 --prefs-show                                        Show saved user or preset options

So basically you can completely manage saved prefs without having to manually edit a text file.

I think git config allows similar things, although it doesn't show you the filename the config came from.