* Notify users that envelope was discarded and retry sending it
* Update Gopkg files with released whisper version
* Forgot to remove signal after refactoring
* Split shhext.tracker into envelopes and mail monitors
* Send envelopes on every new attempt to deliver a message
* Re-send user payloads if previous envelopes weren't acknowledged
* Remove debug api across the codebase
Dmitry Shulyak