Improved Persistence Examples

[jbienzms]

The SA-Persistence sample currently only serializes the spatial graph into a json string or deserializes a json string into a spatial graph. This could be improved to show saving to a file.

In addition, the SA-RefinementBuilding sample does not use persistence. Therefore the alignment is lost between runs of the application.

Recommend creating a new sample based on SA-RefinementBuilding that also implements persistence. A voice command could saves the spatial graph to a text file in the applications isolated storage folder. The next time the application runs the app could check to see if that file exists and load the spatial graph from that file instead of starting new.