debug token sync action

[kacurez]

FIXES #15
provide sync action debugtoken that implments https://developers.facebook.com/docs/graph-api/reference/v2.9/debug_token and returns info about authorized token e.g:
POST https://docker-runner.keboola.com/docker/keboola.ex-facebook/action/debugtoken

{"application":"Keboola Test","expires_at":1498626000,"is_valid":true,"scopes":["user_friends","manage_pages","pages_show_list","ads_management","business_management","public_profile"],"user_id":"128854997588309"}