* Switch mailgun to use webhook api
* Generalize webhook_config_entry_flow
* Add tests for webhook_config_entry_flow
* Add tests for mailgun
* Remove old mailgun file from .coveragerc
* Refactor WebhookFlowHandler into config_entry_flow
* Remove test of helper func from IFTTT
* Lint
* Migrate CONF_WEBHOOK_ID to homeassistant.const
* Switch over all instances of webhook_id to the const
* Switch last instance of webhook_id to the const
* automation: conf constants for conf
* webhook: conf constants for conf
* Pass headers to webhook handler
* Refactors webhook component to post Request object instead of data
* Update webhook tests
* Cleanup webhook test and fix a bug in ifttt
* Address code review comments