fix: Clear dirty UI state across clients on broadcast/multicast user interaction for consistency. #1705

[mturoci]

The root cause of the problem described in the corresponding issue was:

• Client1 renders a form with value.
• UI changes are propagated to the rest of connected clients, (client2).
• UI state is set as dirty in the browser side, due to explicit textbox value. State is same across all clients.
• Client1 clicks the button, q.args with the correct state (btn + textbox) is submitted and cleared.
• UI changes are propagated to all the clients again, but now client1 has fresh UI state, while client2 has the old one still as there was no user interaction that would submit and clear the local args (local state).

This PR sends a clear event to all the connected clients whenever user interaction happens on any of them.

Closes #1705