minor LDAP fixes

ldap: add describtion (full name) during import of a user

(proxy) add option to ignore subnets from getting into the access log (https://github.com/opnsense/core/issues/287)

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.

(ids) add some documentation and reload general settings after download (to show cron after initial download)

fix #282

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....