Deprecating dunst provided script arguments

[fwsmit]

I'm making this issue to discuss deprecating the arguments that dunst provides to scripts in favour of environment variables, as implemented in #802. This would allow users to provide their own arguments to scripts, as suggested in #639. While this is not neccesary, it will be more userfriendly.

[bynect]

any news on this one?

also linked to #1072

[fwsmit]

Currently both options still exist. It's not such a maintenance burden to keep them around, but a 2.0 release might remove them