remove uncessary firmata traffic

Currently it is difficult to use firmata.js with traffic over slower serial transports such as binary websockets.

This change only asks to reporting on existing pins and optionally turns down the sampleInterval before requesting data.


Good question.

When we don't skip the capability query, the default behavior is to tell the board first to turn on REPORT_DIGITAL for every pin, then to turn on REPORT_ANALOG for every pin.

According to http://firmata.org/wiki/V2.2ProtocolDetails the default reporting time is 19ms which is fine for USB, but may be very chatty over a network. 

We may want to call ```board.setSamplingInterval(board.options.samplingInterval);``` whether or not we opt in for ```options.skipCapabilities``` as long as ```options.samplingInterval``` is set because someone could turn on reporting on a specific pin and their samplingInterval rate would be ignored.

I doesn't require a callback.  Perhaps the call to set the sampling rate can be sent right after report version gets back?