Add pulse tweaks

[nkrkv]

Sending pulses in an interactive session is useful, however, they are not so simple. There’s no natural way to send a pulse via Inspector while we are in development mode. So, an extra mechanism is required.

User story

• I put a tweak-pulse node and connect it to a led through flip-flop
• I upload with the debugger and the debug session starts
• Now if I select the tweak-pulse its input box with disabled “pulse” placeholder gets replaced with a button “pulse” in the Inspector
• Clicking the button I toggle my LED on and off

Acceptance criteria

• The basic scenario works as described
• The node is available under xod/debug
• Node’s color behaves as for other tweaks
• The button replaces text input only while the debug session is active and its tab is selected

[evgenykochetkov]

After #1681 implementing this is much easier