Don't import all adapters in adapters package

I've added an adapters.__all__ attribute so that adapters can be
imported individually.
Start web adapter

Can only send statements in, crashes on gustafobot.py:138
Get WebAdapter up to interaction level

Seems a bit crufty to me, but it's now failing on RespondGossip state.
Add Twisted to requirements.txt
Merge upstream branch 'master' into webadapter