Add 'ddd' format option for weekday

[ghost]

No description provided.

[mattberther]

@stefanheine thank you so much for your contribution -- ive been thinking about whether or not we should introduce moment options for date format (which would allow us to leverage all of the options provided by that library).

Would you entertain taking a shot at updating the PR to leverage moment (and provide translations for backward compatibility)?

[mattberther]

Thanks again for your contribution, @stefanheine - Ill open a separate PR for moment options.