[r?] Specification 1.0 implementation

**rebased against latest development and ready for review!**

- [x] Validate old assertions
- [x] Use `info` from validation response instead of the `remote` library.
- [x] Validate new assertions (including signed assertions)
- [x] Ensure compatible output from displayer API
- [x] Use `openbadges-bakery` instead of `lib/baker`