Default event message to group message
Support for sending back Retry-After header when being rate limited
Allow setting config path in configure call

This way when configuring programmatically like:

```python
from sentry.utils.runner import configure
configure()
```

You can set the config file path:
```python
from sentry.utils.runner import configure
configure('path/to/config')
```
Merge pull request #1167 from jisaacks/master

Allow setting config path in configure call
Merge branch 'master' into es