Simple example using ImageSensor region

Setups a simple Network and runs it on the MNIST dataset. Assumes you have the mnist data in subdirectories called mnist/training and mnist/testing.

The current network, using a random SP, gets about 94% correct on the test
set if trained with the full training set.

Fixes #48
Merge branch 'master' of github.com:numenta/nupic.research into simple_image_test
Merge pull request #67 from subutai/simple_image_test

Simple image test