This updates most urlopen() call in the codebase to take in state

from the Certificate Manager, giving them support for managed

certificate verification and mTLS authentication.
By default, urlopen() behaves as it always has, but if there are

custom certificates or CAs configured for the server or Local Site,

they'll automatically pick them up.
The following call sites have been updated:

Security checks
rb-site website communication
WebHooks
Common SCMTool HTTP code

Hosting services have not been updated in this change. That's a larger

piece of work, and is split off into its own change.

Unit tests pass.