Imagemagick 7 Compatibility

We will probably need to add configuration + UI to allow site admins to specify which IM version is in use, 6 or 7, then build the command line conditionally. Or have 3 suites to select from, Imagemagick 6, Imagemagick 7 and GraphicsMagick. Besides the change in the name of the executable binary, there are other chnages in the cmdline arguments that potentially are impacted, see https://imagemagick.org/script/porting.php#cli

I've rerolled the patch for 8.x-3.x for those who want it :-)

Crikey.. identation problem in schema.yml
Ignore #10

Automatically closed - issue fixed for 2 weeks with no activity.