Fix fast sending of multiple group commands
Fix fast sending of multiple group commands

The limit is 6 parallel in a 'burst'. Each command needs ~1 second
to be processed.

Mainly addresses https://github.com/dresden-elektronik/deconz-rest-plugin/issues/212

dresden-elektronik/deconz-rest-plugin,dresden-elektronik/deconz-rest-plugin,dresden-elektronik/deconz-rest-plugin,dresden-elektronik/deconz-rest-plugin,dresden-elektronik/deconz-rest-plugin