Added pulling mode to iotgridd

Hi Robert,

This is the pulling mode I added for the demo. Please review the changes before merge. Sample usage for pulling stateVector every 1 second from "2000::121f:e0ff:fe12:1d0c":

./iotgridd -p 2000::121f:e0ff:fe12:1d0c -t 1000

[Notes]
- It can be extended to use multiple boards/IPs
- It requires curses lib for linking