The /admin panel will now always return an uncached
application setting to ensure it always has the most
current info.

Updating multiple application settings panels through
a single action causes the incorrect action to be shown
when there are errors.  Instead, make each panel action
handle both updating and display.

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

Try to simplify feature flag checks by using policies

There are two cluster hierarchies one for the deployment platform and
one for controllers. The main difference is that deployment platforms do
not check user permissions and only return the first match.

Instance level clusters were already mostly supported, this change adds
admin area controllers for cluster CRUD

Store Let's Encrypt account email in application settings
Also add explicit terms of service consent