Remove abstractmethod for MycroftSkill.stop()
Remove abstractmethod for MycroftSkill.stop()

The MycroftSkill.stop() method does not need to be implemented by the majority of skills, no reason to 'require' its implementation with an abstractmethod.
MycroftAI/mycroft-core,MycroftAI/mycroft-core,forslund/mycroft-core,Dark5ide/mycroft-core,forslund/mycroft-core,Dark5ide/mycroft-core