implicit requirement of twisted rather than asyncio

[FirefighterBlu3]

crossbar blows up with an import error if you try to use asyncio instead of twisted:

#from autobahn.twisted.wamp   import ApplicationSession
from autobahn.asyncio.wamp   import ApplicationSession

  File "/usr/lib/python3.5/site-packages/crossbar-0.11.1-py3.5.egg/crossbar/worker/__init__.py", line 63, in _appsession_loader
    u"crossbar.error.class_import_failed", "session not derived of ApplicationSession"
autobahn.wamp.exception.ApplicationError: ApplicationError('crossbar.error.class_import_failed', args = ('session not derived of ApplicationSession',), kwargs = {})

[oberstet]

To use Autobahn/asyncio based components, these must be run in guest workers. Running components in container workers or side-by-side with router workers requires Twisted

[meejah]

See also this txaio bug which will give you a nicer error-message when it's fixed: crossbario/txaio#42

(Maybe we could provide an even-better error message from crossbar and/or improve the docs)