[hdpowerview] Support for Duette shades

For Duette shades, the top position of the shade is also steerable, but this is not supported by the binding.

Supporting this is only a matter of a new channel and adding a parameter position2in the json body, like this:

{"shade": {"id": 63778, "positions": {"position1": 0, "posKind1": 1, "position2": 1000, "posKind2": 2}}}

and POSTing this json to http://powerviewhub/api/shades/63778

posKind2: 2 is important to get it to work.

(and interpreting this position2 while polling).

[mstroeve]

I just created a bounty for this issue https://www.bountysource.com/issues/67368673-hdpowerview-support-for-duette-shades.

[andrewfg]

I am doing some other work on this binding at the moment => @berland and @mstroeve are you still interested in having this enhancement? If so, are you willing to test it for me, since I do not have any Duette shades myself?