Extract acme double to helper
Create ACME challanges for pages domains
* Create order & challange through API
* save them to database
* request challenge validation
We're saving order and challenge as one entity,
that wouldn't be correct if we would order certificates for
several domains simultaneously, but we always order certificate
per domain
Add controller for processing acme challenges redirected from pages
Don't save acme challenge url - we don't use it
Validate acme challenge attributes
Encrypt private_key in acme orders
Part of adding Let's Encrypt certificates for pages domains
Add acme-client gem
Client is being initialized by private key stored in secrets.yml
Let's Encrypt account is being created lazily.
If it's already created, Acme::Client just gets account_kid by
calling new_account method
Make Let's Encrypt client an instance
Wrap order and challenge classes
