Redo PropPing

* Break PropPing into three items (PropPing stub, UDPPing and GCMPing)
* Adding docs
Merge branch 'feature/config_to_toml' of github.com:mozilla-services/pushgo into feature/config_to_toml
Issue #38

* Break the proprietary stuff into components
* removed gcm cruft from app
* made the code more selfless
R?s

* Fixup Interface calls
* cleanup get/set for propping application/handlers
* correct comments
* TODO: convert storage calls to be more effcient.
Removed duplicate propping section
Swap IPropPing to PropPing
Git Interfaces are tagged

* *-er (Reader, Writer, Logger, etc-er)
Merge pull request #43 from jrconlin/issue38

Issue38 - break proprietary ping into proper component