We need a session object in order to build a session from a
PreKeyWhisperMessage, so add an empty one when none exists on receiving
a message.

Warning: this will break right now if the session can not be constructed
from the received message.There will be an invalid session which will
break if we try to send using it.

This can be used later in order to display trust status of messages, as
well as for potential resending of messages in case of preKey conflicts.

Bundles are now fetched on demand when a session needs to be
established. This should lessen the chance of changes to the bundles
occuring before they're used, as well as lessen the load of fetching
bundles.

Also, the message encryption is now done in a background thread, as this
can be somewhat costly if many sessions are present. This is probably
not going to be an issue in real use, but it's good practice anyway.

Merge prekeys into bundle node

Don't leak cursors, initially create tables

This really sucks to do it like this. Sorry. :(

Can now fetch/retrieve from PEP, as well as encode/decode messages

Numerous fixes

Initial sketch of the peripheral storage infrastructure for the new
axolotl-based encryption scheme.

fixed another typo

Fixed broken URL.

fixed typo

The HTTPS server is throwing GitHub's certificate instead of a proper one, so I'm going to stick with HTTP for now.