When a user needs to use the web configurator, import the the user from the remote ldap server using "import users" on system_usermanager.php
For backward compatibility purposes ldap_backed still can authenticate without a local user, although the web config isn't usable then.
(this always costs an extra query to determine the distinguished name of the user)
We may need to consider if "authenticate only" should be a bit more explicit to the user, or choose to always import users into OPNsense....

(legacy) first step in transition of /themes/ to /ui/themes/  to glue both new and old components better together.
The old /themes/ directory should eventually be removed when all references are gone.

As an added benefit, (default) will now always revert back to the
actual default from the sample configuration, which is exactly
how it should be.

o Makes live-mounting easier as the package config samples won't
  be clobbered anymore.

o Automatically picks up ".in" files, runs replace and moves them
  to their permanent location.

o Refactored src directory install while at it.

Services -> DHCP Server

This reverts commit 92a5f77a.
This reverts commit 681f654c.