Enable initial admin account in example config

The example etc/mudpy.yaml, intended for demonstration purposes,
only binds a listening socket on the loopback interface so shouldn't
be exposed remotely. As a result, turn on the configuration option
to enable elevating the account named "admin" to administrative
privileges automatically upon creation. This allows to run tests of
admin-specific commands with the example configuration.

Also rename the "testadmin" account used by the selftest to match
the name of the default for consistency, and rename test_config.yaml
to test_daemon.yaml reflecting its primary purpose (and also to open
the way for additional test configs as well).