new functionality for plotting connectivity

Hi. I have made some changes to some of the plotting functions which I thought would be worth adding to the main fieldtrip distribution.
The main change is an overhaul of the multiplotCC function. 
Other changes allow the plotting of a computing and plotting of a summerised connectiivty measure using hte stnadard plotting functions. 

If you have any questions or concerns please let me know.

Many thanks

Mark Drakesmith