Note: Messages with OTR advertisement shouldn't be considered encrypted.

gotr expects fjid to be str, but it can be nbxmpp.JID. Converting to str
shouldn't hurt, although could as well call fjid.getStripped() instead
of gajim.get_jid_without_resource.

Traceback (most recent call last):
  File "/usr/lib64/python2.7/site-packages/gajim/common/ged.py", line 93, in raise_event
    if handler(*args, **kwargs):
  File "/home/livid/.local/share/gajim/plugins/gotr/otrmodule.py", line 564, in handle_incoming_msg
    appdata={'thread':event.session.thread_id if event.session else None})
  File "/home/livid/.local/share/gajim/plugins/gotr/potr/context.py", line 210, in receiveMessage
    self.crypto.handleAKE(message, appdata=appdata)
  File "/home/livid/.local/share/gajim/plugins/gotr/potr/crypt.py", line 282, in handleAKE
    outMsg = self.ake.handleRevealSig(inMsg)
  File "/home/livid/.local/share/gajim/plugins/gotr/potr/crypt.py", line 420, in handleRevealSig
    self.onSuccess(self)
  File "/home/livid/.local/share/gajim/plugins/gotr/potr/crypt.py", line 316, in goEncrypted
    self.ctx._wentEncrypted()
  File "/home/livid/.local/share/gajim/plugins/gotr/potr/context.py", line 313, in _wentEncrypted
    self.setState(STATE_ENCRYPTED)
  File "/home/livid/.local/share/gajim/plugins/gotr/otrmodule.py", line 175, in setState
    OtrPlugin.update_otr(self.peer, self.user.accountname)
  File "/home/livid/.local/share/gajim/plugins/gotr/otrmodule.py", line 521, in update_otr
    ctrl = cls.get_control(user, acc)
  File "/home/livid/.local/share/gajim/plugins/gotr/otrmodule.py", line 535, in get_control
    gajim.get_jid_without_resource(fjid), account)
  File "/usr/lib64/python2.7/site-packages/gajim/common/gajim.py", line 297, in get_jid_without_resource
    return jid.split('/')[0]
AttributeError: JID instance has no attribute 'split'

In case we get XHTML in OTR message for some reason (e.g. from gajim
0.16.4), we will see that instead of decrypted content, if we don't
delete existing html first.

This doesn't touch old code in handle_outgoing_msg (which will get exectued
gajim<0.16.4). That should work between versions,
given handle_incoming_msg will overwrite any XHTML in
OTR-encrypted message.

I.e. whitespace-pattern advertisement

Trying to import non-existent common.xmpp would trigger an exception were it
not for a a side-effect of demandimport that Gajim uses. It's not nice to rely
on it in gotr and juick.

juick does not use nbxmpp for anything. Let's just drop the import.

whiteboard does a Gajim version check that no other plugin does.

nbxmpp has been required since Gajim 0.16. In all plugins let's just assume
it's available. Some plugins already do that.