registry: load config from GRL_CONFIG_PATH_VAR if set
This is a simple way to share a GrlConfig between multiple applications. The environment is set by the user and it should not conflict with applications cache if any.
This should have been a follow up from 6ebd283d Not sure if a library like grilo could have a single cache for the config file for all applications (per-user) to share but at least with a environment var should be possible to tweak it.
I've just tested with a new api-key from grl-guardianvideos.lua