Convert config loading to TOML, refactor appropriately

This PR refactors SimplePush to use TOML config loading, changes the existing portions to a new Application based init system, and config loading for each section similar to heka's.

A variety of Go idiom portions were also cleaned up, the logger was factored into an extensible logger with a uniform interface.

Fixes Issue #35.

Awaiting r+ from @jrconlin, @rafrombrc.
I [cleaned this up](https://github.com/mozilla-services/pushgo/blob/pluggable-storage/src/mozilla.org/simplepush/server.go#L263-296) a bit...with a `goto`. :scream: