Fix SkillUpdater creator
Fix SkillUpdater creator

- Since the bus emitter is currently not necessary it's set as an optional
parameter.
- Add proper class docstring

MycroftAI/mycroft-core,forslund/mycroft-core,forslund/mycroft-core,Dark5ide/mycroft-core,MycroftAI/mycroft-core,Dark5ide/mycroft-core