[#141] Send "Cache-Control: no-cache" for admin API responses

- Added a default flag to the base API route, `is_apigility_admin_api`
- Added a "finish" event listener that tests for the above flag in the
  route matches, and, if present, sets a `Cache-Control` header with a
  value of `no-cache`.
Merge branch 'hotfix/141'

Close #141