Create SP Mixin #64

@chetan51 @subutai 

I have created a mixin monitor class for the spatial pooler. Currently the following metrics are collected
1. Indices of active column
2. Active duty cycle of each column
3. Total number of connections.

Let me know if more metrics are desired to be collected.


Change line to `self._mmTraces["connections"] = CountsTrace(self, "connections")`

It should be a `CountsTrace`, not an `IndicesTrace`. And the fact that it's a "total number" is indicated by the fact that it's an `CountsTrace`, so you don't have to include the text "total number".