Make post endpoint pluggable
First go at pickup notifications
Add logger and correct logging in ping
Refactor zot_finger

Refactor zot_finger to reuse it for fingering on channel hashes.
Trim test case for finger without any arguments
More work on notify and pickup
Exception handling inside zot_zot
Refactoring to reduce code duplication

* Reducing duplicate code in network operations.
* Simplifying the related exception handling chain.
* Introduce strict session for handling POST redirects by
  keeping the request method for POST and reissue the same request
  body.
* Depend on the (just released) latest version of Requests library.
* Remove zot_ prefix on functions.
* Created convenience function for AES decapsulation of JSON data,
  which also reduces code duplication and simplifies the related
  exception handling.
Put comment back on Bleichenbacher's attack

Also maked the flow of result easier to look at in the code of AES decapsulate
json.
Tweak verify sender and get hub
ZODB4 has been released last month
Fix unbound variable
Make pluggable framework for message types
Tweak message delivery plugins
Merge branch 'master' into messaging

To continue work on storage for messaging.