Fork hosting_ssl

We ran into some limitations in hosting_ssl that mean that we'd need to implement various workarounds and hacks to get Let's Encrypt working properly. We decided to modernize hosting_ssl (renaming it to hosting_https, in the process). This should allow us to both use it in Aegir 3, and then have a drop-in replacement for Aegir 4.

We're renaming this project to hosting_https, and moving hosting_certificate to be a module within it.

For the meta issue, see [meta] Let's encrypt support.