Indicate in springwolf-ui when no bindings have been defined

[timonback]

Describe the feature request
Some kind of hint/message/notification to signal to the user that a channel operation is missing a binding.
May be only deactivated by default and activated via a url debug flag.

Motivation
When no binding is defined, the ui renders very badly and the user does not know why.
Also, publishing obviously does not work.

Technical details
The action should be triggered when the binding of the operation (publish/subscribe) of any channel does not contain any entries.

Describe alternatives you've considered
Different ux solutions are possible

[timonback]

Relates to #507