initial experiments for a WIP skill permissions model

converse:
- configurable default timeout
- timeout override per skill
- configurable max consecutive number of skill activations
- max consecutive number of skill activations override per skill

fallback:

- fallback skill priority override (user defines fallback order)
- no fallback priority limit (can go above 100 now)
   * No hard limit at priority 100, while not officially supported mycroft-lib can handle fallback priorities up to 999