Add status queries to the skill process

[forslund]

Description

mycroft.skills.is_alive: The service is started and priority skills are
loaded.
mycroft.skills.all_loaded: All skills on the system has been loaded.

How to test

Check the return of self.bus.wait_for_response(Message('mycroft.skills.is_alive')) and self.bus.wait_for_response(Message('mycroft.skills.all_loaded')) from a skill.

Contributor license agreement signed?

CLA [ Yes ]

[forslund]

An alternative could be to have single mycroft.skills.status returning a data structure

{
  "priority_loaded": true,
  "all_loaded": true
}

[davidwagnerkc]

Works as advertised 👍 Maybe we could move to your suggested mycroft.skills.status if we end up having more state like this that might need to be queried. For now with just these 2 key confirmations I think this is good.

[forslund]

Agreed. Merging