overzealous find/replace
get clear_output callback properly
test clear_output callback
move comm.js to base
add message metadata to comm and kernel.send_shell_message
s/init_widgets/init_comms
mention payload source key in execute_result
move comm.js to kernel service
attach comm_manager to kernel
make parent_header available from the Shell object
set parent header properly in comm messages
Added widget output area
Add widget subarea style