Add option to lazily create observables

[jrsearles]

I added a lazy option to only create underlying observables once a property is accessed. This was included as a performance boost for what might be an edge case. I was running into cases in our application where very wide sets of data were being tracked and many of the fields aren't being accessed at all. Lazily creating the observables was a huge performance boost in those cases.

[archangel-irk]

Thank you very much. Forgive me that I so long did.