deck_setkey: <key> | <text> | <colour>

Given that a Streamdeck is connected to the Wintermute PC, sets the given numbered key to the relevant text and colour.

• key is the number of the key on the Streamdeck; if multiple Streamdecks are connected, they are treated as one large device.
• text is the text to set the key to display.
• colour is the colour to set the key to.

Wintermute is quite smart at keeping a dictionary of keys it has previously rendered.