Simplify fedmsg-relay usage.

Currently, in order to send messages to a fedmsg-relay daemon, you have
to initialize with something like this:

```python
fedmsg.publish(topic='blah', active=True, name='relay_inbound', msg={
    'foo': 'bar',
})
```

I've been trying to simplify this over time.  This commit should make
the ``name`` kwarg redundant so you can just specify:

```python
fedmsg.publish(topic='blah', active=True, msg={
    'foo': 'bar',
})
```