_header.h.e: added link to /chat
_message_form.h.e: added form for chat messaging as a temporary placeholder
chat.h.e: render _message_form
channels_controller.rb: have #create action publish an infrastructure-channel message instead of rendering a new view
chat.h.e: change ol.channels to ul.channels; add ul.messages
_message_form.h.e: added IDs and made default url an empty string
_infrastructure.h.e: added #append and click handler
application.rb: require 'net/http' for channels controller