add disable "echo input to output" on all UI modules

[ahonoe]

It would be very helpful to be able to disable the output of UI modules (perhaps all modules) when their value is changed via the input. When this flag is set, the output value of the module can only be set using the UI yet the current value of the module can still be set via its input.

This would be really, really useful.

[senso]

I need to think about this suggestion.
It seems to be a little tricky?