agent: Allow DBus calls without a proxy present

We allow DBus calls to arbitrary objects without a proxy in the
Object Managere.

Closes #523
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
agent: Inform client of byte order.

So that it can know what to do with numbers that are in "network byte
order", for example.
web: Fix 'interfaceAdded'

by passing the correct data to the DBusInterface constructor.
Reverting "agent: Don't omit standard interfaces with the fake ObjectManager."
web: Add 'changeProperties' method to DBusInterface.

So that we can use other sources of change notifications, such as
explicit GetAll calls or custom PropertiesChanged signals.
web: Directly talk to NetworkManager.

Fixes #453
daemon: Remove networking API.
web: More documentation for DBusClient.