Dialog/TooltipDialog: specify default button

[bill]

Forms can be submitted via hitting the return key (there's a default button associated w/the return key).

Can this be done for dialog? If it can be, example files (and documentation) should be updated. If not, then feature should be added.

Not sure how it would work though, something about encasing stuff in a <form> tag I guess, perhaps that should be part of the Dialog template. Need to investigate.

Taken from IBM Design Leadership recommendations.