Overwrite Plugin subscription by user-defined subscription

[mschlenstedt]

Some plugins define a full subscription with a file in their config folder: mqtt_subscriptions.cfg

This "automatic" subscription should be ignored if the user defines his own (maybe limited) subscription in the MQTT Widget GUI.

Example:

The Debmatic (Homematic) Plugin provides an automated subscription to hm/#. This results in hundrets of subscribed topics. Some users define limited subscriptions in the MQTT Widget, like:

hm/status/+/PRESENCE_DETECTION_STATE/#

But the automated subscription to hm/# overwrides this setting.