Issue38 - break proprietary ping into proper component

* removed gcm cruft from app
* added "default" for LoadExtensibleSection to allow for less app preconfig

@bbangert I think I grok what you've done. r?
If we're going to support multiple forms of proprietary pings, having a single selectable one isn't going to be sufficient. We'll need to allow for multiple ones to be configured at once, probably:
```ini
[propping.gcm]
enabled = true
#gcm_config_values

[propping.udp]
enabled = false
#various udp options
```

Then each one can be configured, multiple at a time as needed (if we eventually do iOS push stuff). Are we going to support multiple ones at once, or is this something that should only ever have just one?