new BOSHDispatcher (in dispatcher_nb), improved BOSHClient class, minor changes in other xmpp modules

moved bosh code from client_nb.py to bosh.py, replaced debug logging with debug.py by logging in whole xmpppy (debug.py is now unused)

moved TLS and SSL classes from transports_nb to new tls_nb module, fixed HTTP CONNECT proxy transport

in Client now
- Added NonBlockingHttpBOSH transport (to tranports_nb) and BOSHClient
(to client_nb)
- Extended possible proxy types in configuration by "BOSH" proxy
- Rewrote NonBlockingTLS to invoke success callback only after successful TLS handshake is over (formerly, the TLS Plugin returned right after sending <starttls>)

added prototype of BOSHClient class and script for usage example, removed import of common.gajim from transports_nb

 * always adjust account toggle state
 * try to eliminate extra adjustmants to group state
 * small function renaming

make pep work, move config options per account, make publish_tune configurable in account context menu. fixes #3954

Evens were not properly removed.

 * update documentation and fix indentation
 * don't remove offline contacts from roster when we open the last pending, non chat message event
 * store account and jid per event

auto_join_bookmarks only join non-opened groupchats. Opened one are already auto-joined on re-connection. Fixes #3891

fix tooltip about logging encrypting messages. (it is now shorter, better understood (jargon removed where possible), and we it's OpenPGP and not just GPG guys {or last time I checked :$})

@bct: When moving the OTR stuff, you would've needed to adjust the
XHTML killing part. This patch fixes it. I didn't even notice since
I have XHTML disabled globally.

fixes #3963

fixes #3961

fixes #3950