[Create] Fix layout for create dialog, nasa/mct#161

Reduces space consumed by create/cancel buttons in
object creation wizard, and adds padding (by way of
an empty border) around the dialog to match that
seen in UE specs for dialogs (see MCT-2788 on
private issue tracker for example.)
Merge pull request #162 from VWoeltjen/mct161

[Create] Fix layout for create dialog, nasa/mct#161