added Potjans2014 to examples

Added a complete pyNN script simulating the model published in Cerebral Cortex,2014:
http://cercor.oxfordjournals.org/content/24/3/785.short

The examples comprises several pyNN scripts to run the model as well as python script to create a job script and submit it to the queue of a compute cluster. The down-scaled version should run on a laptop as well. 

Has only been tested with the pyNN.nest backend.