Add live updates to dashboard widget

[frankiejarrett]

We should allow live updates to occur in the dashboard widget just as we do on the Stream Records screen.

1. It should bring in new records using the Heartbeat API.
2. The number of records visible should always match the Records per page value, as new records enter the widget, older ones should move to the next page(s).
3. It should be enabled by default if there is no value for it found in the DB.

[johnregan3]

@fjarrett, do you want a separate Screen Options (text input/checkbox) for this, or just use the value set on the Post List page?

[frankiejarrett]

@johnregan3 Not sure what you mean, this is for the Dashboard widget configuration.

[johnregan3]

@fjarrett Ok. I think you answered my question. You want this set in the Screen Options panel (that slides down from the top of the page, just like on the Stream list page), right?

[frankiejarrett]

@johnregan3 No, we want another field added to the Configure section of the widget.