[Enhancement] Adding moment computed fixes #6

This PR is dependent on #9.  Will squash once you thumbs up and merge #9 .
The way we use date values in our Yahoo app, they're often bound to UI components (i.e., a date picker), so being writable by default would make the most sense. 

Occasionally we have things like the createdAt, updatedAt fields, but in our app, these are the exceptions not the rule.

This app is just one more data point, but food for thought :)