Integrate wi-fi button in the demo

[vvasco]

Following the discussion reported in #250, we want to use a wi-fi button for triggering speech and integrate it in the demo. We decided to go for this one. I ordered it today, it should be arriving in 3 -5 days.

[vvasco]

Button arrived!

[vvasco]

Done in #280. The button was configured to produce a http POST request when pressed once (see #264). The POST request is managed by node-button.js, which creates a server receiving requests and sending triggers to /managerTUG/cmd:rpc, by means of yarp.js.

For the demo with the real robot, managerTUG is in charge of deciding if the trigger is a start or a stop:

• the first trigger received is assumed to be a start;
• if the time occurred between two consecutive triggers is higher than min-timeout, the trigger is a start (/stop) if the previous was a stop (/start);
• if no trigger is received after a start within max-timeout, a stop is sent.