Initial work for the AES cipher class

This is based somewhat loosely on how Keyczar does things. Their
implementation does things in a much more generic way to allow for more
variance in how the cipher is created, but since we're only using one
key type most of our values are hard-coded. They also add a header to
their messages, which I am not doing (don't see the need for it
currently).
Initial commit for the "fireball2" connection plugin

Still needs:
* chunked file transfer/receive
* should probably move all send/recv operations to separate
  functions to reduce code duplication
* initial connection setup over ssh? or do we handle that in runner?
Fireball2 mode working!