Phs/mk 124 schema tools

Finish our typing and add a validation tool.

The `askari` command line tool is now a [thor](http://whatisthor.com/) app.  It has one command, `validate`, which looks for `config/askari.yml` (or the passed path) and validates it as a `Askari::Schema::V0::Application`.

A schema has been added to the example app (following the structure laid out in deployment acceptance test) and we now prove it validates.