Add ability to pass error string back to datagrid

This adds the ability for the data source for a datagrid to signal
that an error occurred fetching the data and provide an error message
to display to the user.

As error is signaled by passing a string as the first argument to
the callback function instead of an object. The passed string is the
HTML to add to the table for the error message.
resolving merge conflicts
Merge branch 'dougwilson-feature/datagrid-error-state' into 2.5.0-wip