Add -imdkit config to toggle imdkit at runtime

[amosbird]

See discussion in #2123

[DaveDavenport]

Thanks!!
maybe 'imdkit' is better then 'enable-imdkit'.. because now it is:

-enable-imdkit

and

-no-enable-imdkit

if you f.e. want to override config file.

[amosbird]

Oh, sure!