Add settings for simple NS cards

[cascer1]

With all the fields we're adding to the Nightscout cards, some users might prefer simple cards that contain only BG data.

diabot ns setsimple <true/false>

[PaperT1D]

I'm not sure how many different fields are being added or will eventually be added but, if there are going to be several, maybe also have the option to set which fields display? Something like..

diabot ns setdisplay <trend cob>

..which would enable the trend and carbs on board fields, and disable any others (such as insulin on board).